Les services écosystémiques (SE) sont définis comme les bénéfices que les humains retirent des écosystèmes. A titre illustratif, un arbre peut produire des fruits, séquestre du carbone et différentes activités récréatives ou valeurs esthétiques lui sont liées. Parmi les différentes approches d’évaluation des SE, la matrice de capacité est une méthode considérée comme flexible et rapide à mettre en œuvre. Constituée d’une table d’allocation d’un score pour chaque SE et chaque écosystème considéré, elle est de plus en plus utilisée en France, ainsi qu’à l’international. Dans le cadre de cette thèse nous avons travaillés sur l’évaluation des scores à dire d’experts dans le but, notamment, de déterminer certains biais et limites méthodologiques, mais également d’explorer des développements innovants pour différentes applications sur le Parc Naturel Région Scarpe-Escaut et la Région Hauts-de-France. Enfin nous avons intégré les disservices (les effets indésirables de la nature sur l’Homme) et l’intégrité écologique (la condition/santé de l’écosystème) dans l’évaluation des SE afin d’avoir une vision plus complète de la relation homme-nature / Ecosystem services (ES) are the benefits that humans derive from ecosystems. For example, a tree produces fruit that we pick, sequesters carbon as it grows, supports various recreational activities and has aesthetic value. Among the different approaches developed to assess ES, the experts-based capacity matrix is flexible and quick to implement. The matrix is a look-up table that assigns each ecosystem type a score defined by experts expressing its ES capacity. It is increasingly used in France, Europe and internationally. Three themes are addressed in the thesis: (i) methodological analysis to define and specify limits and specify methodology to address them, (ii) application of the method to the Scarpe-Escaut Regional Natural Park and to the Hauts-de-France Region, and (iii) integration of the evaluation of disservices (undesired effects of the natural environment on humans) and ecological integrity (condition/health of the ecosystem) into the evaluation of ES to take fuller account of the relation between humans and their natural environment.

Atmospheric N deposition is becoming a stressor on ecosystems in the western U.S. There are few National Atmospheric Deposition Program (NADP) monitoring sites and little is known about N deposition impacts on terrestrial ecosystems in the Intermountain West. Alpine ecosystems may be particularly sensitive to changes in N inputs because of the shallow soils, short growing seasons, and sparse plant cover. This study focused on N deposition effects on an alpine ecosystem in Grand Teton National Park located along a modeled N deposition gradient (Moose Basin high, Paint Brush Medium, Rendezvous Mtn. low) and across contrasting edaphic conditions using a two-factorial design. At each location, we estimated N deposition and measured soil moisture and temperature across edaphic conditions, soil parameters (total and extractable N, available N, net mineralization, and nitrification potential), and plant community characteristics (species richness, species composition, percent cover, plant and root biomass, N content, and above and belowground plant components). These response variables were used to test whether there is a north to south N deposition gradient, if N deposition and N status are affected by soil moisture content, and whether soil and/or plant properties were affected by N deposition and edaphic conditions and if the response variables can serve as indicators as early warning signs of N saturation. The Tetons receive 1.42 kg N ha-1 yr-1 with more in winter (0.85-1.17 kg N ha-1 yr-1) than during the summer (0.25 kg N ha-1 yr-1). Soil moisture content was related to snowpack accumulations and melt but did not affect N status. Moose Basin (i.e., high N deposition) showed characteristics of an N-rich site shown by higher soil N content and extractable soil NH4+, higher nitrification potential, low C:N ratios, more aboveground biomass, and higher foliar N content compared to the RDV location. Rendezvous Mountain (i.e., low N deposition) showed characteristics of an N-poor site having lower soil extractable N, high C:N ratios in soil and roots, and low N mineralization potential. Paint Brush was highly variable in soil and plant characteristics and most clearly showed differences between wet and dry sites. In terms of N status, it was intermediate and shared similarities with both N-poor and N-rich sites. This study shows that it is important to consider both soil and plant indicators (i.e., total and extractable N in soils, soil nitrification potential, above and belowground biomass, and N content) together to assess N status. The C:N ratio of plants and soils was less informative than anticipated. Species richness and composition was a less sensitive indicator of N-induced change and should be considered for long-term assessments only.

Heterogeneous spatial and temporal distributions of soil resources important to plant growth have been documented in the sagebrush steppe ecosystem. There can exist as much variability in soil resources within the root zone of individual plants as exists across an entire field. The objective of this dissertation research was to evaluate how plants respond to, utilize and influence the spatial heterogeneity of soil resources. The three specific sets of questions addressed are outlined in the three main chapters of this dissertation. My first study addressed how the number and concentration of phosphorus (P) patches in the root zone of an individual Artemisiaplant influenced the ability of the plant to increase root P uptake capacity from the enriched patches as compared to roots from unenriched soil. I found that root uptake kinetics in the most enriched patches in general was not limited by the number or concentration of phosphorus patches experienced by the plant. However, the plants could modulate the quantity of P acquired from a target patch as the number of patches experienced increased. My second study addressed how six species common to the Great Basin, which represent three different growth forms, utilized nitrogen (N) from patches or a uniform distribution. The two species within the two perennial growth forms, shrub and tussock grass, revealed different capacities for acquiring N from concentrated patches immediately adjacent to a plant and from N applications at a distance from plants. This suggests the potential for different root foraging behavior. The two annual species used concentrated N patches more effectively than uniform applications. My third study described decimeter scale variability of soil water potential (Ψs) in the interspace of two perennial plants at different time scales and at different soil moisture conditions. The mean Ψs was more spatially consistent in the interspace between plants during a midsummer dry period compared to an early summer period. Diel Ψs fluctuations during an early summer dry period was more spatially consistent than a midsummer dry period. When soil moisture was recharged by precipitation there were no spatial diel patterns and the mean Ψs was autocorrelated across the area evaluated.

Une meilleure connaissance des variations saisonnières et interannuelles du cycle du carbone dans en Amazonie est essentielle afin de comprendre le rôle de cet écosystème dans le changement climatique. La modélisation atmosphérique inverse est un outil puissant pour estimer ces variations, en exploitant l'information sur la distribution spatiale et temporelle des flux de CO2 en surface contenue dans des observations de CO2 atmosphériques. Néanmoins, la confiance en les estimations des flux en Amazonie obtenues à partir des systèmes d'inversion mondiale est faible du fait du manque d'observations dans cette région.Dans ce contexte, j'ai d'abord analysé en détail les estimations de l'échange net de CO2 entre la biosphère et l'atmosphère (NEE) générées par deux inversions mondiales pour la période 2002 — 2010. Ces deux inversions ont assimilé des données provenant du réseau mondial d'observation du CO2 atmosphérique hors de l’Amérique du Sud, et une d'elles a assimilé des observations de quatre stations de surface en Amazonie, qui n'ont jamais été exploitées dans les études d'inversion précédentes. J'ai montré que dans une inversion mondiale les observations de stations loin d'Amazonie et les observations locales contrôlaient la NEE. Pourtant, les résultats ont révélé des structures à très grande échelle peu réalistes. L'analyse a confirmé le manque de stations en Amazonie pour fournir des estimations fiables, et les limites des systèmes d’inversion mondiale avec des modèles à très basse résolution.J'ai donc ensuite évalué l'apport de l'utilisation du modèle atmosphérique régional BRAMS, par rapport à celle du système mondial de prévision météorologique ECMWF, pour le forçage météorologique du modèle de transport atmosphérique CHIMERE simulant le CO2 en Amérique du Sud à haute résolution (~35 km). J'ai simulé le CO2 avec les deux modèles de transport―CHIMERE-BRAMS et CHIMERE-ECMWF. J'ai évalué ces simulations avec les profils verticaux de mesures aéroportées, en analysant les mesures individuelles et les gradients horizontaux de CO2 calculés entre paires de stations dans le sens du vent, à différentes altitudes ou intégrés sur la verticale. Les deux modèles de transport ont simulé les observations de CO2 avec une performance similaire, mais j'ai trouvé une importante incertitude sur les modèles de transport. Les mesures individuelles et les gradients horizontaux ont été surtout sensibles à la NEE, mais aussi, pendant la saison sèche, aux émissions des feux de biomasse (EFIRE). J'ai trouvé que l'assimilation des gradients horizontaux était plus approprié pour les inversions que celle des mesures individuelles, étant donné que les premiers ont été moins sensibles au signal associé aux flux hors de l'Amérique du Sud et à l'incertitude sur le modèle de transport en altitude.Finalement, j'ai développé deux systèmes d'inversion régionale pour l'Amérique du Sud tropicale avec les deux modèles de transport, et j'ai lancé des inversions avec quatre types de vecteurs d'observation: de mesures individuelles et gradients horizontaux sur cinq niveaux verticaux, à la surface, ou de gradients horizontaux intégrés sur la verticale. J'ai trouvé une forte dépendance des estimations des bilans régionaux et sub-régionaux de NEE et EFIRE au modèle de transport, ainsi qu'au vecteur d'observation. Les inversions assimilant des gradients horizontaux ont séparé mieux les signaux de NEE et EFIRE. Cependant, les grandes incertitudes sur les flux inversés ont réduit la confiance en ces estimations. Par conséquent, si mon étude n'a pas amélioré la connaissance des variations saisonnières et interannuelles de la NEE en Amazonie, elle a montré les besoins d'amélioration de la modélisation du transport dans la région et de la stratégie de modélisation inverse, du moins à travers une définition du vecteur d'observation appropriée qui prenne en compte les caractéristiques des données disponibles, et les limitations des modèles de transport actuels. / A better knowledge of the seasonal and inter-annual variations of the Amazon carbon cycle is critical to understand the influence of this terrestrial ecosystem on climate change. Atmospheric inverse modeling is a powerful tool to estimate these variations by extracting the information on the spatio-temporal patterns of surface CO2 fluxes contained in observations of atmospheric CO2. However, the confidence in the Amazon flux estimates obtained from global inversion frameworks is low, given the scarcity of observations in this region.In this context, I started by analyzing in detail the Amazon net ecosystem exchange (NEE) inferred with two global inversions over the period 2002 — 2010. Both inversions assimilated data from the global observation network outside Amazonia, and one of them also assimilated data from four stations in Amazonia that had not been used in previous inversion efforts. I demonstrated that in a global inversion the observations from sites distant from Amazonia, as well as local observations, controlled the NEE inferred through the inversion. The inferred fluxes revealed large-scale structures likely not consistent with the actual NEE in Amazonia. This analysis confirmed the lack of observation sites in Amazonia to provide reliable flux estimates, and exposed the limitations of global frameworks, using low-resolution models to quantify regional fluxes. This limitations justified developing a regional approach.Then I evaluated the benefit of the regional atmospheric model BRAMS, relative to the global forecast system ECMWF, when both models provided the meteorological fields to drive the atmospheric transport model CHIMERE to simulate CO2 transport in tropical South America at high resolution (~35 km). I simulated the CO2 distribution with both transport models―CHIMERE-BRAMS and CHIMERE-ECMWF. I evaluated the model simulations with aircraft measurements in vertical profiles, analyzing the concentrations associated to the individual measurements, but also with horizontal gradients along wind direction between pairs of sites at different altitudes, or vertically integrated. Both transport models simulated the CO2 observations with similar performance, but I found a strong impact of the uncertainty in the transport models. Both individual measurements and horizontal gradients were most sensitive to NEE, but also to biomass burning CO2 emissions (EFIRE) in the dry season. I found that horizontal gradients were more suitable for inversions than individual measurements, since the former were less sensitive fluxes outside South America and further decreased the impact of the transport model uncertainty in altitude.Finally, I developed two analytical regional inversion systems for tropical South America, driven with CHIMERE-BRAMS and CHIMERE-ECMWF, and made inversions with four observation vectors: individual concentration measurements and horizontal gradients at five vertical levels, close to the surface, or horizontal gradients vertically integrated. I found a strong dependency of the inverted regional and sub-regional NEE and EFIRE emissions budgets on both the transport model and the observation vector. Inversions with gradients yielded a better separation of NEE and EFIRE signals. However, the large uncertainties in the inverted fluxes, did not yield high confidence in the estimates. Therefore, even though my study did not improve the knowledge of seasonal and year-to-year variations of the NEE in Amazonia, it demonstrated need of further efforts to improve transport modeling in the region and the inverse modeling strategy, at least through a careful definition of the observation vector that accounts for the characteristics of the available data, and the limitations of the current transport models.

Folksägner, historier och sagor har länge gett olika djur mänskliga attribut och gestaltat djuren på ett människoliknande sätt. Vargen är inget undantag och återges allt som oftast på ett negativt sätt. Kan dessa erfarenheter av vargen från sagornas värld drabba hur elever tänker om vargen och dess roll i ett ekosystem och samspelet med andra organismer? Undersökningens syfte är att belysa elevers tankar attityder om vargen samt hur de placerar in dess roll i ett ekosystem med ett jämförande förhållningssätt mellan elever från stadsmiljö och landsbygdsmiljö. En reviderad klinisk intervjumetod i grupp har använts för att uppnå syftet med studien. Totalt har 18 elever deltagit, varav fem från landsbygden och 12 elever från stadsmiljö. Undersökningen visar att eleverna från stadsmiljö har en negativ attityd till vargen, vilket skiljer sig från eleverna från landsbygden som har en positiv alternativt neutral attityd till varg. Eleverna från de båda geografiskt skilda områdena beskriver vargens roll i ett ekosystem ur ett antropocentriskt och teleologiskt synsätt i ungefär lika stor utsträckning. / For many years folklore, stories and fairy tales have been giving animals human attributes and elaborated the animals in a human-like way. The wolf is no exception and is often reproduced in a negative way. Can these experiences of the wolf from the selection of fairy tales affect how pupils think about the wolf and its role in an ecosystem? And furthermore, can it affect how the pupils understand how the wolf interacts with other organisms? With a comparative approach between pupils from urban and rural environments, the purpose of the study is to elucidate thoughts and attitudes toward the wolf and to emphasize how pupils place the wolf and its role in an ecosystem. A revised clinical group interview method has been used to achieve the purpose of the study. In total, 18 pupils participated, five of them from the countryside and 12 pupils from a city. The survey shows that pupils from the urban environment have a negative attitude toward the wolf, which differs from the pupils from rural areas, who have a positive, alternatively neutral attitude towards the wolf. The pupils from both urban and rural environments describe the role of the wolf in an ecosystem in an anthropocentric and teleological approach to an approximately equal extent.

Les services écosystémiques (SE) désignent les bénéfices fournis par les écosystèmes à la société. En France, la législation cherche à les intégrer dans les études d’impact environnemental avec la promulgation de la Loi pour la reconquête de la biodiversité, de la nature et des paysages (2016). Pour ce faire, il est nécessaire de développer des méthodes de terrain d’estimation des SE. C’est dans ce cadre qu’une collaboration entre le Laboratoire d’Ecologie Alpine et le bureau d’études EGIS Environnement a vu le jour, afin de répondre à la question : comment quantifier les SE à l’échelle locale ?Pour cela, nous avons étudié deux SE de régulation régulièrement évoqués dans le contexte du changement global. Le service de pollinisation est essentiel pour l’alimentation humaine et est au cœur de l’actualité de par les déclins des populations d’insectes pollinisateurs. Le SE de régulation du climat global par la séquestration de carbone par les écosystèmes est d’intérêt majeur en regard des changements climatiques récents et annoncés.Nous avons suivi les quatre étapes du développement d’un protocole. Premièrement, pour le SE de pollinisation entomophile qui possède de nombreuses définitions dans la littérature, nous avons établi par une revue bibliographique un cadre conceptuel afin de définir le SE de pollinisation et d’identifier les indicateurs et leurs méthodes de mesures. Nous avons choisi pour la suite d’adopter la définition du SE de pollinisation comme la capacité de l’écosystème à soutenir la pollinisation entomophile, i.e. la présence d’insectes pollinisateurs. Deuxièmement, nous avons abordé la question du choix des indicateurs pour l’estimation de ce SE. En effet, la capacité du SE de pollinisation peut être estimée par des indicateurs directs, liés à la présence des insectes pollinisateurs sur la parcelle, et des indicateurs indirects, liés aux ressources d’alimentation et de nidification sur la parcelle d’étude et dans le paysage. Nous avons comparé les mesures de ces deux types d’indicateurs estimés en vergers et en prairies. Les objectifs étaient de tester la cohérence entre ces deux types d’indicateurs pour le SE de pollinisation et la possibilité d’une simplification du protocole d’estimation en la basant uniquement sur des indicateurs indirects. Les indicateurs indirects n’expliquaient pas une part suffisante de la variabilité observée dans les mesures d’abondance et de richesse des pollinisateurs pour permettre simplification du protocole.Troisièmement, nous avons cherché à simplifier le protocole d’estimation du SE de la régulation du climat global par la mesure des stocks de carbone en prairies et en forêts. Pour cela, nous avons comparé les estimations obtenues par des protocoles simplifiés à celles obtenues par un protocole plus complet et mesuré les incertitudes causées par ces simplifications. Le protocole d’estimation a pu ainsi être simplifié pour les deux compartiments de l’écosystème stockant le plus de carbone : la biomasse aérienne en forêt et le carbone organique du sol. Enfin, afin de tester l’applicabilité du protocole simplifié d’estimation du SE de régulation du climat global, nous l’avons testé sur des parcelles de zones humides, des écosystèmes stockant une grande quantité de carbone. Ces parcelles ont été placées dans un modèle d’états-et-transitions afin de tester si les mesures de gestion peuvent affecter les stocks de carbone des zones humides. Les actions de gestion sur la biomasse aérienne changeaient les stocks de carbone entre les zones humides herbacées et forestières. Le stock de carbone organique du sol, stock majeur dans les zones humides, ne différait pas entre les différents états étudiés, reflétant la difficulté d’agir sur ce compartiment.Cette étude montre que le développement méthodologique pour la quantification de SE sur le terrain peut mener à des protocoles simples et fiables mais que le processus de développement est différent selon les SE abordés. / Ecosystem services are benefits supplied by ecosystem to human societies. In France, recent legislation aims to include ecosystem service in environmental impact studies with the enactment of the Law for the recovery of biodiversity, nature and landscapes (2016). To do so, it is necessary to develop field methods for ecosystem service estimation. In this setting, a collaboration was established between the Laboratoire d’Ecologie Alpine and the environmental consultancy EGIS Environnement to answer the following question: how can ecosystem services be quantified at local scale?We studied two ecosystem services often cited in the global change context. The pollination service is essential for human food production. Given worldwide pollinator declines it is at the centre of scientific, citizen and political concerns. The service of global climate regulation by carbon sequestration by ecosystems is of major interest given the recent and coming climate changes.We investigated four key steps for developing a field protocol. First, the ecosystem service of entomophilous pollination has numerous definitions in the scientific literature. Thus, based on a literature review we built a conceptual framework for defining the pollination service and identifying quantifiable indicators and their measurement methods. We chose to define the pollination service as the ecosystem capacity to support entomophilous pollination, i.e. pollinating insect presence. Second, we worked on indicator selection for the pollination service estimation. Pollination capacity can be estimated through direct indicators linked to pollinator presence on the plot and through indirect indicators linked to feeding and nesting resources in the plot and in the landscape. We compared measures of these two types of indicators within orchards and grasslands. Our aims were to test consistency between both indicator types for the pollination service and the possibility of protocol simplification based on indirect indicators. Indirect indicators did not explain enough of the observed variability in pollinator abundance and richness to allow a protocol simplification.Third, we tried to simplify the estimation protocol of the ecosystem service of global climate regulation from measures of carbon stocks in grasslands and forests. We compared estimations obtained by simplified protocols to estimations obtained by a more complete protocol. We also quantified the uncertainties caused by these simplifications. The estimation protocol could be simplified for the two most important carbon pools: aboveground biomass in forests and soil organic carbon. Finally, to test the applicability of the simplified protocol of carbon stock estimations, we applied it on wetland plots. These plots were organized following in a state-and-transition model to test whether management decisions are likely to affect wetland carbon stocks. Management actions on aboveground biomass changed carbon stocks between herbaceous and forested wetland. Soil organic carbon, the major carbon stock in wetlands, was unchanged between the different studied stats, illustrating the difficulty to manage soil carbon stocks in the short term.This study shows that method development for field quantification of ecosystem service can lead to simple and reliable protocols. However, the development process is different for each ecosystem service.

Mesopelagic (open ocean, 200-1000 m depth) fishes are important consumers of zooplankton and are prey of oceanic predators. Some mesopelagic fishes (e.g., myctophids and stomiids) undertake a diel vertical migration where they ascend to the near-surface waters during the night to feed and descend into the depths during the day to avoid predators. Other mesopelagic fishes (e.g., Sternoptyx spp.) do not vertically migrate and remain at deep depths throughout the day. While in the epipelagic zone (surface – 200 m depth), vertically migrating fishes become prey to upper-trophic level predators, such as: tunas and billfishes. Benthic fishes (e.g., macrourids) often vertically migrate as well, ascending into the pelagic zone to feed on pelagic organisms. Fishes of different depths and vertical migration habits likely have a different ecological role in food webs. The relationship between parasites and gut contents provides insights into ecological processes occurring within assemblages, as prey items are often vectors for parasites. This study examined the differences between the prey items present in the gastrointestinal cavity and parasites of 26 mesopelagic fish species in the Gulf of Mexico. Results showed that based on the proportionally dominant prey items per species, six different feeding guilds existed within this assemblage, five based on planktivory: copepodivores, predators of copepods and other zooplankton, predators of copepods and euphausiids, gelatinivores, generalists, crustacean decapodivores, and upper-trophic level predators. Larger fishes preyed on larger prey items and harbored more parasites. Sigmops elongatus exhibited an ontogenetic diet shift at 75 mm standard length, progressing from eating primarily copepods at small sizes to eating primarily euphausiids at large sizes. Compared to similar studies, this study revealed a higher parasitic infestation by trematodes, an endoparasite (parasite within the host) class often restricted to nearshore hosts, in Gulf of Mexico fishes. Helicometrina nimia, the dominant parasite of the gempylid Nealotus tripes, has not previously been recorded in hosts below 200 m depth, suggesting a foodweb pathway that transitions from nearshore to offshore. These data can be used to develop and refine models aimed at understanding ecosystem structure and connectivity.

Marine bioeroders, borers, and burrowers can have drastic effects to marine habitats and facilities. By physically altering the structure of marine habitats, these organisms may elicit ecosystem-level effects that cascade through the community. While borer damage is typically restricted to a few substratum types, burrowing isopods in the genus Sphaeroma attack a diversity of substrata in tropical and temperate systems. My dissertation examined how boring sphaeromatid isopods affect coastal habitats (saltmarshes, mangroves) and other estuarine substrata as well as marine structures. I used a combination of lab and mensurative field experiments to quantify the effects of boring by isopods and examine how select factors affect the colonization, hence burrowing damage by isopods. I explored these questions primarily using the temperate boring sphaeromatid, Sphaeroma quoianum, as a model organism. My initial lab experiments quantified the per capita erosion rates of S. quoianum in four commonly attacked estuarine substrata. I found marsh banks and Styrofoam substrata were the most affected per capita. I supplemented this lab experiment with a year-long mensurative field experiment examining how erosion rates differ between marshes infested and uninfested by boring isopods. Marshes infested with isopods eroded 300% faster than uninfested marshes. I further examined the boring effects on Styrofoam floats. I compiled surveys and observations and conducted a short experiment to describe how isopods affect Styrofoam floats used in floating docks. I observed dense colonies of isopods attacking floats and expelling millions of plastic particles in the ocean. The boring effects to simulated Styrofoam floats were also affected by seawater temperature. Burrowing effects in Styrofoam floats exhibited a curvilinear relationship with temperature and peaked around 18°C. These results suggest a 1-2°C increase in water temperature could increase boring effects 5-17% of populations of isopods in Oregon and California bays. To examine the small-scale factors that mediate colonization and boring, I conducted a series of binary choice experiments. I found the presence of conspecifics, biofilm, and shade were important factors influencing colonization. These small scale factors likely explain why isopod attack is focused in some substrata. Finally, to examine the boring effects of tropical isopods in mangroves, I examined the associations between burrowing by S. terebrans and mangrove performance and fecundity. I found negative relationships between boring effects and performance and fecundity in two mangrove species in a restored mangrove stand in Taiwan. Together, these studies elucidate the effects of bioerosive isopods on saltmarshes, mangroves, and marine structures. However, the similar mechanisms involved in bioerosion in other boring species suggest that these results can be used to infer similar effects of other borers. In addition, since many species of sphaeromatid isopods have been introduced, this research shows how the effects of a non-native bioeroder can damage marine facilities and degrade and alter marine habitats. Through biological erosion and thus changing the physical structure of a marine habitat these non-native species can have ecosystem-level effects that cascade throughout the local community.

Magister Scientiae (Integrated Water Resource Management) / River catchments in agricultural areas are strongly influenced by runoff from cultivated or grazed fields, and nutrient loading of these fields can result in large quantities of nitrates and phosphates being transported to rivers in surface runoff. In intensively farmed areas, nutrient loading is often so high that large quantities of nitrates and phosphates are transported to streams in surface runoff. Within these areas, strips of natural riparian vegetation and wetlands are critical in providing nutrient uptake functions that can reduce the load entering streams. A wetland can be a source, sink or transformer of nutrients, where fine sediments such as silt and clay have the ability to store and trap considerable amounts of phosphorus through adsorption and precipitation processes. Therefore, the determination of phosphorus adsorbed to fine sediment is important in understanding the role and value of wetlands in agricultural landscapes, and is the main focus of this study. The aim of the study is to evaluate an indicator-based approach, WET-EcoServices, to assess wetland sediment and phosphate trapping, through comparison with field survey data. The study focuses on spatial analysis and field survey of three Hydrogeomorphological (HGM) units classified for the Wiesdrift wetland on the Nuwejaars River, Cape Agulhas. The three HGM units are classified as: a floodplain wetland at the inlet of the system, a channelled valley-bottom wetland towards the middle part of the system and a floodplain wetland towards the outlet of the system. In-field observations were recorded for hydrogeomorphic and vegetation characteristics for each HGM Unit. AstroTurf mat sediment samples, grabbed channel bed and floodplain sediment samples were analysed for particle size and orthophosphate concentrations, while suspended sediment masses were recorded from three pairs of time-integrated sediment samplers located near the inlet, near the middle, and near the outlet of the wetland. Statistical analysis showed that orthophosphate concentrations are associated with fine sediment. Thus, the orthophosphate concentrations follow the distribution of silt on the Wiesdrift wetland. The dominant vegetation along transect 2, at which the highest concentrations of orthophosphate was found, is occupied by Typha capensis and Cyperus textilis. The percentage of fine sediment (silt) ranged between 0-37%, where the remaining percentage was sand. There was also a significant positive correlation between orthophosphate concentration and silt (Spearman’s rank-order correlation: rs = 0.692, N = 70, P < .001). The largest total sediment amount was found at Outlet 1 and Outlet 2 in the HGM unit 3 of the Wiesdrift wetland, with a value of 0.653 g. Overall, orthophosphate concentrations ranged between 0 mg/kg and 31320 mg/kg within the Wiesdrift wetland. WET-EcoServices determines an average score for phosphate trapping from on-site indicators such as hydrological zones, vegetation structure and soil texture/permeability. The dispersal of fine sediment and associated adsorbed phosphate is more complex than can be determined by a tool like WET-EcoServices because the tool captures the long-term mean conditions of a wetland system that determines the overall uptake of phosphates over extended time periods, thus future wetland assessments is recommended to take place over a longer period than this study. However, the field results of orthophosphate distribution are generally consistent with the findings from WET-EcoServices, further motivating for the use of the tool in wetland management applications.

No description available.