As atividades agrícolas, principalmente as monoculturas, exigem grande utilização de insumos. A aplicação constante de defensivos agrícolas, como herbicidas, pesticidas e fungicidas, tem promovido crescentes impactos sobre os recursos hídricos e biota neles presentes, principalmente em organismos não alvo dessas substâncias. O presente estudo teve como principal objetivo avaliar os efeitos do fungicida Pyrimethanil na comunidade de macroinvertebrados bentônicos, por meio do monitoramento ambiental em unidades experimentais de campo (mesocosmos) e ensaios ecotoxicológicos laboratoriais com indivíduos da espécie Chironomus sancticaroli. Os mesocosmos foram construídos utilizando-se seis caixas de água com volume equivalente a 1500 litros. A contaminação dos mesocosmos com Pyrimethanil foi realizada por meio de pulverização direta na superfície da água aplicando-se uma concentração equivalente a 0,1 mg/L de Pyrimethanil nos mesocosmos contaminados. Dessa maneira, os mesocosmos foram divididos em três réplicas contaminadas e três réplicas controles. O monitoramento e coleta de amostras de água e macroinvertebrados bentônicos foram realizados com frequência mensal, durante o período de um ano. O fungicida Pyrimethanil não ocasionou alterações significativas nas variáveis monitoradas. Da mesma forma, a estrutura comunitária de macroinvertebrados bentônicos apresentou características semelhantes entre os mesocosmos contaminados e controles. Entretanto, durante o monitoramento, os mesocosmos controles apresentaram valores significativamente mais elevados na abundância de indivíduos e quantidade total de táxons quando comparados aos valores observados nos mesocosmos contaminados com Pyrimethanil. / Agricultural activities, mainly monocultures, require large use of inputs. The constant application of agrochemicals, as herbicides, pesticides and fungicides, has promoted impacts on water resources and biota at the center, especially on non-target organisms such substances. This study aimed to evaluate the effects of fungicide Pyrimethanil in benthic macroinvertebrate community through environmental monitoring experimental units of field (mesocosms) and laboratory ecotoxicological tests with individuals of Chironomus sancticaroli. The mesocosms were made using six tanks with maximum volume equivalent to 1500 liters. The contamination of the tanks with Pyrimethanil was performed by spraying of water on the surface by applying a fungicide concentration equivalent to 0,1 mg/L. Thus, the mesocosms were divided into three contaminated replicas and three controls replicas. The monitoring and sampling of water and benthic macroinvertebrates were performed on a monthly basis during the period of one year. The fungicide Pyrimethanil does not cause significant changes in monitored variables. Similarly, the community structure of benthic macroinvertebrates were similar characteristics between the contaminated and control mesocosms. However, during the monitoring, the mesocosms controls had significantly higher values in the abundance of individuals and total number of taxa compared to the values observed in the mesocosms contaminated with Pyrimethanil.

Investigations were made examining the relationships between gastropod species richness and abundance across 20 phosphate and 20 natural lakes in Central Florida. In additional to lake category, age of phosphate lakes was used to determine if phosphate lakes ever approximate natural lakes. Additional physical, chemical, and biological parameters, including chlorophyll a, Ca, secchi, phosphorous, conductance, fish predation, and recreational lake use were investigated in order to determine if they affected gastropods with lake age. Comparisons were also made between gastropod species richness and average abundance and two groups of dominant vegetation categories: Panicum, a structurally complex macrophyte, and Typha, a less structurally complex macrophyte. After phosphate mining operations are completed, Florida state regulations require the establishment of ecologically viable habitat (created lakes) which reflects the properties of regional natural lakes including vegetation structure, littoral zone, bank slope, and lake depth. The littoral zone is part of the mandated structure of the lake, and is of considerable importance to the uptake, storage, transformation and release of nutrients. Within the littoral zone, gastropods are a critical link in the food web with implications for the long term structure and function of a lake. They are known for their close associations with macrophytes and are common environmental indicators since they have limited mobility, high diversity, are well studied, are representative of their habitat type and have a widespread geographic range. They are also an important food sources for many predators in aquatic environments, include migratory waterfowl and game fish. Gastropod species richness and abundance data were collected via standard net sweep methodology. Abundance was presented in catch per unit effort, therefore all abundance data were averages. Initial comparisons between gastropod species richness and average abundance yielded no significant differences between natural and phosphate lakes. However, when age was applied as a covariate, there was a significant difference between lake age as a continuous variable in species richness comparisons. Additionally, categorical comparisons between lakes older or younger than 30 years indicated significantly higher species richness and average abundance of gastropods in lakes phosphate lakes older than 30 years. Physical and chemical properties of the lakes did not appear to influence gastropod populations between lakes of different ages. Fish predation interactions did not indicate any significant influence either. However, the presence of boat ramps did indicate a positive relationship between average gastropod abundance and species richness and recreational lake use. Littoral zone macrophyte comparisons between dominant vegetation Typha and Panicum indicated a significantly positive relationship between gastropod species richness and average abundance in older phosphate lakes dominated by the more structurally complex Panicum macrophytes. Confidence in the Typha and Panicum results was confounded by lack of access to younger, Typha dominated, phosphate lakes. An increase in sample size for younger Typha lakes, with additional site access, may further support these findings.

As global change alters the chemical and physical dynamics of the ocean, it is increasingly necessary to determine ecological responses across environmental gradients. The benthic ecosystems of fjords often contain a multitude of environmental gradients conducive to multivariate field studies. In this thesis, I describe the benthic community structure of two British Columbian fjords in relation to markedly different environmental variables. In Chapter 2, I show a strong correlation between suspension-feeder abundance and flow structure on the steep fjord walls of Douglas Channel, BC. I also describe distinct assemblages with depth and with location along the fjord head-mouth axis. Using a suite of biological traits, I show that the deep portion (> 400 m depth) of the most seaward site is the most taxonomically and functionally diverse in the fjord. My results suggest fjord walls form an expansive ecosystem containing diverse and dense assemblages of suspension feeders relevant to the flow of energy through fjord basins and as biodiversity reservoirs. In Chapter 3, I extend a long-term hypoxia time-series (2006 -2016) to document the response of soft-bottom epibenthic megafauna of Saanich Inlet, BC to a prolonged hypoxic event in 2016 that caused abundance declines, community aggregation and shifts in species composition more extreme than those seen in the 2013 hypoxia cycle. I also assess community threshold responses along the oxygen gradient; I found community transitions consistent across years and with Northeast Pacific oxygen thresholds based in ecophysiological studies. Taken together, these studies show a strong coupling between oceanographic conditions and the community structure of fjord benthos. I suggest that climate-driven alterations in North Pacific oceanographic regimes may portend major changes in fjord ecosystems. / Graduate

O método de Caracterização Fisionômica de Comunidades Marinhas Bentônicas propõe o uso da unidade operacional chamada Povoamento aliada à amostragem fotográfica. Dentre as 4 abordagens do método, o objetivo do Capítulo 2 foi testar a precisão da abordagem quantitativa quando submetida a: a) diferentes pesquisadores e b) diferentes análises realizadas pelo mesmo pesquisador. A análise de correspondência (CA), baseada no recobrimento percentual obtido em cada situação, não mostrou diferenças significativas entre os valores encontrados para os Eixos I, II, III e IV (correspondentes a 42.8% da variabilidade dos dados) quando comparados por ANOVA (p= 0.963; 0,975; 0.867; 0.894, respectivamente). Os resultados apresentados no Capítulo 2 indicam que a etapa quantitativa do Método de Caracterização Fisionômica de Comunidades Marinhas Bentônicas é pouco subjetiva. No Capítulo 3, as posições geográficas de cada povoamento foram registradas com um GPS durante duas coletas (julho/2005 e janeiro/2006). Essas posições foram inseridas na base de mapas do Google Earth com auxílio do programa GPS Track Maker. Foram registrados 41 povoamentos, sendo a maior fração (36,6%) representada por povoamentos que possuem organismos do Filo Rhodophyta como espécies dominantes. Em seguida, cada um dos Filos Chlorophyta e Ochrophyta representou 17,1% dos povoamentos. Os povoamentos cujas espécies dominantes pertencem ao grupo dos animais compuseram 29,3%; com o Filo Cnidaria apresentando a maior fração de povoamentos (12,2%) e Porifera a menor (2,4%). A posição de todos os povoamentos é apresentada em um mapa integral das comunidades marinhas bentônicas de substrato consolidado da região entre-marés da Ilha do Francês, Espírito Santo. O Capítulo 4 teve como propósito descrever quantitativamente as comunidades marinhas bentônicas do médio-litoral da Ilha do Francês. A partir de observações realizadas durante o Capítulo 3, foram selecionadas três áreas que mostraram as principais variações não biológicas (exposição aos ventos predominantes, exposição ao batimento de ondas, inclinação e a orientação). Uma coleta preliminar (julho de 2005) revelou que as comunidades do médio-litoral da Ilha do Francês podem ser divididas em duas grandes faixas. Em uma das faixas, o povoamento dominante foi Banco de Chthamalus (78,6%) enquanto na outra os povoamentos dominantes foram Tapete de Amphiroa e Jania (32,8%), Banco de Dictyota (16,5%) e Banco de Perna (16,7%). Nas coletas seguintes (Janeiro e Julho de 2006) a estratégia de distribuição dos elementos amostrais foi aleatória estratificada. Na faixa de algas, tanto no verão quanto no inverno, Tapete de Jania e Amphiroa foi o povoamento que apresentou os maiores recobrimentos percentuais médios na Área 1 (39% e 66,2%, respectivamente). Na Área 2 os povoamentos Banco de Dictyota (27,8%) e Tapete de Centroceras e Ceramium (28,7%) obtiveram os maiores recobrimentos médios durante o verão, enquanto no inverno o maior valor obtido foi o de Tapete de Amphiroa e Jania (55%). Na Área 4 Banco de Perna apresentou maior recobrimento médio durante o verão (43,2%) e Banco de Dictyota na coleta de inverno (29,4%). Na faixa de cracas Banco de Chthamalus apresentou maior recobrimento percentual médio em todas as áreas e épocas amostradas. Nas Áreas 1 e 2 a média do recobrimento desse povoamento apresentou maiores valores durante o inverno (87,9% e 64,6% respectivamente), enquanto na Área 4 no verão (80,7%). Espera-se que os Capítulos 3 e 4 juntos possam subsidiar acompanhamentos das condições das comunidades da Ilha do Francês, estudos de outros aspectos dessas comunidades e também o trabalho de órgãos ambientais. O Capítulo 5 tem como foco avaliar a precisão relativa de três variações (20, 50 e 100 pontos) das técnicas de pontos aleatórios aplicada à análise de imagens para comunidades marinhas bentônicas. Diferenças estatísticas entre valores de porcentagem de cobertura das diferentes técnicas foram verificadas por análise de correspondência (CA) e os valores obtidos para os dois eixos de maior variabilidade, foram testados por ANOVA. Os testes estatísticos não demonstraram diferenças quantitativa e qualitativa comparando 50 e 100 pontos aleatórios à Segmentação Manual. É possível concluir aqui que 50 ou mais pontos para análise de comunidades marinhas bentônicas fornecem dados qualitativos e quantitativos precisos. Este trabalho, além de demonstrar que o uso dos povoamentos é preciso, descreve as comunidades do médio-litoral da Ilha do Francês qualitativamente e quantitativamente. Essa descrição poderá, a partir de agora, constituir o ponto de partida para o monitoramento e o gerenciamento desse ambiente frente ao crescimento econômico esperado nos próximos anos para a região. O mapeamento dessas comunidades pode, ainda, subsidiar outros aspectos de pesquisa como, por exemplo, os experimentais. Entretanto, é fundamental ainda o estudo do infralitoral do local. A inclusão desses dados complementará e poderá alterar as conclusões que obtivemos neste trabalho acerca da diversidade e dos grupos dominantes, permitindo uma visão global das comunidades bentônicas da Ilha do Francês. / The method Physiognomic Assessment of Hard Bottom Marine Benthic Communities proposes the use of operational units called settlements, allied to photographic sampling. Among the 4 approaches of this method, the Chapter 2 aimed to test the precision of the quantitative one when submitted to: a) different researchers and b) different time analysis carried out by the same researcher. The correspondence analysis (CA) based on the percent cover showed no significant differences between values found for the Axes I, II, III and IV (corresponding to 42.8 % of data variability) when compared by ANOVA (p = 0.963; 0,975; 0.867; 0.894, respectively). The results presented on Chapter 2 indicate that the quantitative approach of the Physiognomic Assessment Method of Hard Bottom Marine Benthic Communities, is little researcherdependent. On Chapter 3 the geographic position of each settlement was taken with the use of a GPS during two samples (july/2005 and january/2006). These positions were inserted into Google Earth databases with the GPS Track Maker software (version 13.2). Forty one settlements were observed. The largest fraction (36,6%) was represented by Rhodophyta; followed by Chlorophyta and Ochrophyta; The last two represented 17.1% of the total. The settlements dominated by animals represented 29,3% where Cnidaria was the most common group (12,2%) and Porifera the most uncommon one (2,4%). The location of each settlement is presented on a map of the whole hard bottom marine communities located in the intertidal zone of the Francês Island, Espírito Santo state. The Chapter 4 described the hard bottom marine communities from the tidal zone of Francês Island. Using the data mapping presented in Chapter 3, three areas that showed the main non biological variations (predominant winds exposition, waves exposition, slope and orientation) were selected. The preliminary sample (July of 2005) showed that the hard bottom communities from Francês Island can be divided in two great zones. In one zone the dominant settlement is Chthamalus Bed (78.6%) while in the other one the dominants are Amphiroa and Jania Turf (32.8%), Dictyota Bed (16.5%) and Perna Bed (16.7%). For the following samples (2006 January and July) the stratified random sample strategy was chosen. On the seaweed zone, for the area 1, both during summer and winter the Jania and Amphiroa Bed was the settlement with the highest average percent cover (39% and 66.2%, respectively). On area 2, Dictyota Bed (27.8%) and Centroceras and Ceramium Turf (28.7%) showed the highest percent cover during summer while Amphiroa and Jania were predominant (55%) on winter. On area 4 Perna Bed showed a high percentage of coverage during the summer sample (43.2%) and Dictyota Bed during the winter one (29.4%). In barnacles zone Chthamalus Bed was the dominant in all areas and seasons sampled. On areas 1 and 2 this settlement showed the highest values on as 1 during winter (87.9% and 64.6% respectively), while in Area 4 it happened during summer (80.7%). It is expected that Chapters 3 and 4 can subsidize communities monitoring, studies of other aspects of the Frances Island and also the work of environmental managers. The Chapter 5 aims to evaluate the relative precision of three variations (20, 50 and 100 points) of random points technique applied to analyze images for benthic marine communities. Statistical differences between the values of the percentage of coverage of the different techniques, were performed by correspondence analysis (CA), and the values obtained for the two major axes of variability were tested by ANOVA. Statistical tests did not present quantitative and qualitative differences comparing 50 and 100 random points to Manual Segmentation. It is possible to conclude here that the 50 or more points to analyze images of marine benthic communities supply precise qualitative and quantitative data in the case of the studied community. This work, beyond demonstrating the precision of the use of settlements, describes qualitatively and quantitatively the inter-tidal communities from Francês Island. The communities description presented here could constitute a guideline to monitoring possible alterations that can be caused by the economic development of the region. The map presented is an important tool for the Francês Islands management actions, as well as other researches concerning these communities. However, it is still fundamental a study about subtidal communities. The inclusion of these data will complement and could even modify the conclusions that we got here concerning the diversity and the dominant groups, allowing a global vision of the Francês Island benthic communities.

Coral reefs are priority habitats which are vulnerable to natural and anthropogenic disturbances. These can cause phase shifts from coral habitat to degraded algal-dominated states – and consequent changes in the distribution, abundance and activity of associated fish species. In the eastern Red Sea, human-induced reef degradation is likely to increase with planned development of the Saudi Arabian coast and the changing climate. The present study therefore investigates the ecological effects of coral-algal phase shifts in reef-associated fish communities, using naturally occurring within-reef benthic zones as proxies for levels of habitat health - with a focus on how these responses differ temporally. These zones were dominated by: hard coral (coral zone), coral and turf algae (transition zone), and macroalgal canopies (algal zone). Six inshore reef areas, were studied in periods with low and high densities of Sargassum in the algal zones (May and November respectively). Community composition was assessed via visual census and predation activity predicted using two proxies: in situ experiments and biomass of carnivores. In both periods, we observed distinct fish communities in each zone - with reduced species richness, Shannon-Wiener diversity and predation intensity, from the coral to the algal zones. Decreases in the abundance and biomass of fish also occurred from the coral to algal zones in May but a spike, as well as a shift in community composition, occurred in the algal zone in November. This shift is attributed to the vast increases in grazer biomass, predominantly Siganus luridus, associated with the November bloom of Sargassum canopies. The present study established, the composition and functioning of Red Sea fish communities is spatially and temporally affected by increased macroalgal dominance. This finding supports the need for herbivorous fish to be made a conservation priority in the management and conservation of reef systems in order to prevent phase shifts to algal dominated states. We conclude that if Red Sea reefs are allowed to shift to alternate states, depending on the density of macroalgal canopies, reefs may support high biomass and abundance of fish but the functioning of the fish community will be altered and the diversity lost.

Marine unconsolidated sediments, such as sand, gravel and muds, constitute the most extensive benthic ecosystems globally. Biological data for these ecosystems are frequently sparse which can hinder the success and implementation of marine management strategies for benthic ecosystems. There are limited studies in South Africa on benthic epifauna. This study investigates the composition and distribution of epibenthic invertebrate assemblages along the west and south coast of South Africa (sampled using depth-stratified demersal trawls) to inform marine environmental management. Sample depth varied from 36m to 899m. Multivariate tools (PRIMER and PERMANOVA+) were used to analyse spatial (west vs south coast) and temporal (2011 vs 2017) patterns in epifauna. This study also investigated an overlap region between the west and south coast. A group average linkage cluster analysis defined biotopes using significant branching (p< 0.05). Biotopes were compared against the 2012 National Biodiversity Assessment (NBA) benthic habitat map to investigate whether epifaunal biotopes identified, align with the existing classification. A significant difference among epifauna between region and depth was found, where the west coast had a higher average number of individuals and species per station. Sympagarus dimorphus and Pelagia noctiluca were characteristic species for west and south coast respectively. Epifauna was found to be significantly different between 2011 and 2017, with a notable increase in the abundance of Crossaster penicillatus in 2017. The majority of the biotopes aligned with the current NBA classification, in particular the Agulhas Sandy Shelf Edge ecosystem type on the south coast and South Atlantic Upper Bathyal and Namaqua Muddy Inner Shelf ecosystem types on the west coast. This thesis contributes to the mapping and description of offshore ecosystem types to inform marine environmental impact assessments, marine spatial planning and marine protected area expansion.

Exacerbated deep-water hypoxia, brought about by anthropogenic-derived dissolved organic carbon (DOC) input, has potentially detrimental impacts on organisms residing in freshwater ecosystems. Oxygenation of the water column is a potential management strategy to mitigate this impact, and used to alleviate DOC induced oxygen depletion. In this thesis, I investigated the effects of hypolimnic oxygenation on benthic macroinvertebrate and zooplankton biomass and size assemblages in an experimental dystrophic lake. The experiment, which took place between 2017-2020 in a dystrophic brown-water lake consisting of two interconnected basins, was performed according to a Before-After-Control-Impact design. One basin was continuously monitored under reference conditions while the oxygen concentrations of the other basin was experimentally increased halfway through the experimental period. Macroinvertebrates were sampled from the epi-, meta- and hypolimnion while zooplankton were sampled from throughout the water column (0-6 m) and, during 2020, also the hypolimnion (3-6 m) separately. Collected macroinvertebrate and zooplankton samples were analyzed for biomass, chironomid body lengths and zooplankton community compositions per basin and treatment. Mean benthic biomass, chironomid biomass and chironomid body length increased in response to oxygenation in the hypolimnion but no effect was found in the epi- or metalimnion habitats. Observed biomass responses were mainly driven by the increase in chironomid biomass. No differences were found in neither zooplankton community assemblages nor biomass following oxygenation. These results suggest that the lack of oxygen-rich habitats act as a major limiting factor for hypolimnic macroinvertebrates and especially for chironomids. Zooplankton, on the other hand, appear to be limited by resource availability as opposed to the abundance of suitable, oxygen-rich habitats only. The results suggest that oxygenation may have clear benefits for deep-water macroinvertebrates. However, as a management tool, it is ineffective as a means to increase zooplankton abundances.

Understanding how coral reefs respond to natural disturbances is fundamental to assess their resistance and resilience, particularly in a context of climate change. Therefore, and given the escalating frequency and intensity of bleaching events, it is essential to evaluate responses of communities in space and time to disentangle the mechanisms underlying ecological changes. Here, I analyzed a dataset comprising 59 reefs, resulting from 6 years (2014-2016) of a coral reef benthic monitoring program in the Saudi Arabian Red Sea. It encompasses the 2015/2016 mass bleaching event and spans three different geographic regions: north (Duba and Al Wajh), central (Jeddah and Thuwal), and south (Al Lith, Farasan Islands and Farasan Banks). The results indicate significant differences between regions and through time. Coral assemblages from the southern region were the most affected by the 2015 bleaching event, where in some reefs, hard and soft corals cover dropped to <2% in 2017. Important changes in community structure were observed through time in the three regions, with a shift to a macroalgae, turf algae and CCA dominance. Different environmental drivers (salinity, sea surface temperature, fishing index, distance to shore, and photosynthetically active radiation) were analyzed, and highlighted a regionally-based response of the communities to these potential drivers of change. Overall, the examined Red Sea benthic communities presented dynamic patterns in composition. Distance decay plots based on presence/absence showed a general increase in similarity throughout multiple spatial scales in 2019, when compared to previous years. This finding suggests a loss in biodiversity due to thermal anomalies and bleaching events, evidenced by a homogenization (i.e., increase similarity) in the composition of the benthic communities. I document here a patterns of dominance of a few benthic groups with time and a decrease in branching corals. This study provides baseline information about changes in coral reef benthic community structure and identifies environmental factors with a higher impact on a regional scale. This information can be used to guide conservation efforts in these highly biodiverse ecosystems.The resulting datasets can be valuable for anticipating responses of coral communities under future climate scenarios.

Allochthonous organic carbon is increasing and leading to browning of freshwaters in the northern hemisphere. It is already known that an increase in allochthonous dissolved organic carbon (DOC) affects benthic primary production and respiration negatively via light limitation, however, little is known about the impact on benthic bacteria. This report aims at examining how DOC and other environmental variables affect the production and growth of benthic bacteria. This was done by analyzing data from 18 lakes in northern Sweden with different DOC concentrations. This analysis was divided into two datasets: one including data at the whole lake scale and the other including data over depth within the lakes. The result showed that DOC, average depth, and the light extinction coefficient all had a negative impact on bacterial production on a whole lake scale. The light extinction coefficient was also affecting the whole lake bacterial growth efficiency (BGE) negatively. Over depth within the lakes a higher light input increased the bacterial production. In the same dataset, light was also affecting the BGE positively, while temperature had a negative effect. The results can thus be linked to the increase in allochthonous carbon and brownification. Because allochthonous DOC have a negative effect on benthic primary production, there will be less autochthonous DOC available for benthic bacteria. Allochthonous DOC is considered less degradable than autochthonous DOC. The increase in allochthonous DOC therefore has a negative impact on benthic bacterial production, likely connected to a decrease in production of autochthonous DOC by benthic algae.

The effects of a mountain lake on nitrogen dynamics in a sub-alpine watershed were examined via watershed monitoring, mesocosm experiments, microcosm experiments, and enzymatic assays during spring and summer of a single year. Our study addressed the questions: (1) How does hydrologic transport through the lake affect the net fluxes of dissolved nitrogen (N) species? (2) What are the net effects of the littoral zone biota on dissolved N fluxes? (3) What are the seston and benthic uptake rates of nitrate? (4) What is the magnitude of N retention in littoral zone sediments? (5) What role does microbial hydrolysis of amino-groups from organic matter play in the uptake of dissolved nitrogen, relative to rates of nitrate uptake? Our study found a net positive flux of total dissolved N and dissolved organic N (DON), and a net negative flux of nitrate through the lake. During snowmelt, when the majority of nutrients are transported in this watershed, DON was retained in the lake. Several experiments were run to more closely examine the mechanisms behind these observations. Experiments in 2.1 m3 mesocosms in June and July measured rates of DON flux from the littoral zone sediments into the water column that were similar to increments measured in the lake. 15N-nitrate mesocosm and microcosm tracer experiments quantified benthic and pelagic nitrate uptake and retention of that nitrate in the benthic sediments. Areal nitrate uptake was 65-times greater in the sediments than in the water column seston and the turnover rate (half life) of the newly input nitrate pool in the sediments was 33-64 days. Finally, the prevalence of DON relative to dissolved inorganic N (DIN) and high measured rates of enzymatic amino acid hydrolysis suggest the importance of DON as a source of N for this aquatic system.