The effect of environmental conditions upon the growth, production and development of river phytoplankton was investigated for the feeder rivers to the Humber Estuary. The study was part of the Land Ocean Interaction Study LOIS) and focused upon the Rivers Trent and Yorkshire Ouse. The influence of physical, chemical and biological factors upon phytoplankton development were measured through routine fieldwork and laboratory analyses. During fieldwork measurements were collected which complemented measurements collected by LOIS colleagues. Data collected in this study included phytoplankton species composition, density and biomass and is situ rates of growth and production. In situ rates of loss through grazing and respiration were also measured. Laboratory investigations concentrated upon the effects of Ught and temperature upon dominant phytoplankton species and were developed to complement fieldwork. The project focused around four main aims. These were basically to assess the size and composition of phytoplankton maxima in the Trent and Ouse, measure in situ rates of growth and production, estimate losses from grazing and to develop models, using the data collected to assess the effect of environmental conditions upon phytoplankton development and autochthonous carbon in the Humber Estuary. The results showed that phytoplankton dynamics in the Trent and Ouse were controlled primarily by discharge, light and temperature. During spring, when conditions were favourable for growth, rapid phytoplankton growth and maximum rates of production were observed. However, spring floods often interrupted die large phytoplankton populations which developed. Other factors such as grazing and sedimentation were also considered as potentially important in the loss of phytoplankton. The turbid nature of the rivers resulted in a fine balance between photosynflietic gain and respirational loss. This temporal change in environmental conditions resulted in a temporal waxing and waning of the phytoplankton. This in turn had an impact upon the seasonality of the flux of autochthonous carbon to the Humber Estuary. Laboratory investigations and development of a photosynthetic model confirmed the importance of light and temperature upon phytoplankton development in these rivers. In terms of phytoplankton growth and production and the flux of autochthonous carbon, the Trent and Ouse were found to be typical of many other European rivers. The study highlighted the importance of the Trent as a source of autochthonous carbon to the Humber Estuary.

Sponges have important ecological functions on coral reefs because they are regionally abundant, competitively dominant, and process large volumes of seawater. The sponge loop hypothesis proposes that sponges consume dissolved organic carbon (DOC) and then releases the carbon as shed cellular detritus back to the reef benthos. Within this context, we examined the carbon flux mediated by the giant barrel sponge, Xestospongia testudinaria, on reefs in the Red Sea, where sponge abundance is comparatively low relative to coral reefs elsewhere, such as the Caribbean. Seawater samples were collected from the incurrent and excurrent (In-Ex) flow of 40 sponges from inshore, mid-shelf, and offshore reefs between 18° and 22°N latitude off the coast of Saudi Arabia. Concentrations of DOC and living particulate organic carbon (LPOC) were significantly higher in incurrent (ambient) seawater on inshore reefs than mid-shelf and offshore reefs. Consistent with studies of X. muta in the Caribbean, the diet of X. testudinaria is comprised primarily of DOC; mean values of the nutritional components across all sites were 60.5% DOC, 35.7% detritus, and 3.8% LPOC. Taking into account the specific filtration rates of nutritional components and oxygen consumption of sponges across the inshore-offshore gradient, there is evidence (1) of a threshold concentration of DOC below which sponges cease to be net consumers of DOC, and (2) that sponges on offshore reefs are food-limited. Contrary to the sponge loop hypothesis, there was no evidence that X. testudinaria, returned DOC to the benthos in the form of detritus, but was, instead, a net consumer of detritus from the water column. Unlike the cryptic, interstitial sponges that were studied to advance the sponge-loop hypothesis, emergent sponges may have an alternate pathway for returning DOC to the benthos by converting it to sponge biomass rather than sponge detritus.

Soil carbon (C) is the largest terrestrial carbon pool. While inputs to this system are fairly well constrained, the diverse factors driving soil C efflux remain poorly understood. Carbon in surface soils is mobilized via two distinct pathways: CO₂ gas flux and dissolved C flux. The goal of this study was to quantify the role of hydrologic variability in mobilizing carbon as gaseous and dissolved fluxes from near-surface soils, and to determine their relative magnitudes. Data were collected through 2010 and 2011 from two subalpine sites in Arizona and New Mexico. I observed no significant variability in dissolved fluxes, and these values were low at all sites. In contrast, CO₂ fluxes were large (from 0.22 g C m⁻² d⁻¹ to 5.27 g C m⁻² d⁻¹) and varied between sites and between years. My results suggest that in arid montane forests soil carbon flux is critically linked to water availability.

Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km).

Coastal outwelling of organic carbon from mangrove wetlands contributes to near-shore productivity and influences biogeochemical cycling of elements. I used a flume to measure fluxes of dissolved organic carbon (DOC) between a mangrove forest and adjacent tidal creek along Shark River, Florida. Shark River’s hydrology is influenced by diurnal tides and seasonal rainfall and wind patterns. Samplings were made over multiple tidal cycles in 2003 to include dry, wet, and transitional seasons. Surface water [DOC], temperature, salinity, conductivity and pH were significantly different among all sampling periods. [DOC] was highest during the dry season (May), followed by the wet (October) and transitional (December) seasons. Net DOC export was measured in October and December, inferring the mangrove forest is a source of DOC to the adjacent tidal creek during these periods. This trend may be explained by high rates of rainfall, freshwater inflow and subsequent flushing of wetland soils during this period of the year.

Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km).

Climate models forecast lower and less frequent precipitation in the next 50 years. This is especially pronounced in the central United States, where Texas is expected to lose a week’s worth of rain every summer. Water availability is a primary driver of carbon flux in terrestrial ecosystems – controlling photosynthesis and organic matter decomposition. Thus, under proposed rainfall shifts, understanding the potential ecosystem response is key to predicting the future of terrestrial productivity. Terrestrial nutrient cycling is also driven by microbial saprotrophs, which are the chief decomposers of organic matter. Understanding the microbial response to rain shifts is key in predicting the ecosystem response. Research supports both microbial community specialization to local environment, and that the microbial communities may have the ability to rapidly acclimate to environmental change. To address this question of microbial response, we used a steep natural rainfall gradient along the Edwards Plateau in central Texas. The Edwards Plateau is an ideal field site in which to test these ideas because nearly identical grassland habitat and soils are found across its entirety, while mean annual precipitation ranges from 45 cm to 91 cm. To understand how soil microbial communities varied as a result of historical rainfall differences, we divided the gradient into four isoclines based on precipitation (46-56 cm, 56-66 cm, 66-76 cm, and 76-86 cm), and examined soil and soil microbial community characteristics at three sites in each isocline. We further used soils from the same sites for a reciprocal soil moisture experiment, where we asked how soil microbial communities responded to altered moisture conditions. Using a full factorial design, soils from each site in each isocline were exposed to one of four soil moisture treatments: soil moisture from the ‘home’ isocline and the three other ‘away’ isoclines. The moisture treatments were maintained for one year. Microbial respiration was measured at regular intervals throughout the experiment; fungal hyphal abundance and inorganic nitrogen were measured at the final harvest. The soils collected from the gradient decreased in both soil moisture and hyphal abundance from the wet to the dry end of the gradient, but there was no trend in inorganic nitrogen. In the reciprocal moisture experiment, microbial CO2 respiration was affected by both home isocline and soil moisture treatment. Drier sites had a narrower response to wetter treatments and did not achieve the same activity as wetter sites regardless of soil moisture treatment. In contrast, soils from the wettest isocline experienced severe reductions in activity with drying, with activity at the driest moisture treatment below that found in soils that were from the driest isocline. These patterns are consistent with some degree of local specialization, which may constrain the ability of microbial communities to rapidly acclimate to altered precipitation regimes. This experiment did not include immigration, however, and shifts in community composition in the presence of dispersal may be able to counteract local specialization. Given expected future increases in drought intensity microbial decomposition activity is likely to decrease and local specialization may create a lag in acclimation to the new condition. Thus, local specialization of microbial communities should be considered when predicting ecosystem responses to future climate change and their potential feedbacks to ecosystem productivity and carbon storage. / text

With rising salinity levels in many freshwaters across the globe caused by for example sealevel rise and de-icing salts, it becomes important to understand what effect it has on freshwater ecosystems, since the lakes and rivers themselves are important parts in the global carbon cycle. In this study I have looked at what effects increased salinity levels have on different lakes metabolism, specifically oxygen concentration and primary production. The experiment was conducted using mesocosms in three different lakes in Sweden, separated both geographically and by nutrient status (eutrophic, oligotrophic, and dystrophic as well as oligotrophic). The response to increased salinity differed between the lakes; the increased salinity had a strong negative effect on the oligotrophic lake. In general, increased salinity caused a decline in oxygen content, both the maximum value and the amount of diurnal variation, as well as primary production. Therefore, the conclusion is that a rise in salinity will affect lake metabolism in a detrimental way, with a stronger effect on more sensitive lakes. / Med stigande saltnivåer i många sötvatten världen över, orsakade av exempelvis ökande havsnivåer och applicering av vägsalt, blir det viktigt att förstå vilken påverkan detta har på ekosystem i sötvatten då de utgör en viktig del I den globala kolcykeln. I den här studien har jag tittat på vilken effekt förhöjda salthalter har på olika sjöars metabolism, specifikt syrehalt och primärproduktion. Experimentet utfördes med hjälp av mesokosmer i tre olika svenska sjöar, skilda både geografiskt och trofiskt (eutrof, oligotrof samt dystrof och oligotrof). Sjöarnas respons till den ökade salthalten varierade; saltet hade en starkt negativ effekt på den oligotrofa sjön. På en generell nivå så sjönk syrehalten, både maximum värden och dygnsvariationen, samt primärproduktionen vid högre salthalter. Slutsatsen blir därför att ökade saltnivåer kommer att påverka sjöars metabolism negativt, med en starkare effekt på mer känsliga sjöar.

Groundwater chemistry is highly variable and dependent on environmental conditions, and it is not entirely understood how all these factors contribute to groundwater chemistry. This study aims to examine some of the factors that contribute to groundwater heterogeneity in the Amazon Rainforest. This was done by collecting groundwater samples from piezometers in three different regions of the Amazon Basin in Brazil, and then analyzing them in the lab for cations and anions, as well as dissolved inorganic and organic carbon. Environmental conditions were measured in the field using portable probes. The results were analyzed and compared with previously established figures for tropical forests. Statistical analyses were performed using SPSS and R in order to establish correlations and linear relationships between the studied variables.Understanding how groundwater supplies are affected is important for being able to predict and manage environmental change that can degrade groundwater sources. This knowledge could also help in developing strategies for groundwater remediation efforts in areas where supplies are contaminated.

Vegetation community patterns and processes are indicators and integrators of climate. Recently, scientists have shown that climate change is most pronounced in circumpolar regions. Arctic ecosystems have traditionally been sequestering carbon and accumulating large carbon stores. However, given enhanced warming in the Arctic, the potential exists for intensified global climate change if these ecosystems transition from sinks to sources of atmospheric CO2. In the Mid and High Arctic, ecosystems exhibit extreme levels of spatial heterogeneity, particularly at landscape scales. High spatial-resolution (e.g., 4m) remote sensing data capture heterogeneous vegetation patterns of the Arctic landscape and have the potential to model ecosystem biophysical properties and CO2 fluxes. The following conditions are required to model arctic ecosystem processes: (i) unique spectral signatures that correspond to variations in the landscape pattern; (ii) models that transform remote sensing data into derivative values pertaining to the landscape; and (iii) field measures of the variables to calibrate and validate the models. First, this research creates an ecosystem classification scheme through ordination, clustering, and spectral-separability of ground cover data to generate ecologically meaningful and spectrally distinct image classifications. Classifications had overall accuracies between 69% - 79% and Kappa values of 0.54 - 0.69. Secondly, biophysical variable models of percent vegetation cover, aboveground biomass, and soil moisture are calibrated and validated using a k-fold cross-validation linear bivariate regression methodology. Percent vegetation cover and percent soil moisture produce the strongest and most consistent results (r2 ≥ 0.84 and 0.73) across both study sites. Finally, in situ CO2 exchange rate data, an NDVI model for each component flux, which explains between 42% and 95% of the variation at each site, is generated. Analysis of coincidence indicates that a single model for each component flux can be applied, independent of site. This research begins to fill a gap in the application of high spatial-resolution remote sensing data for modelling Arctic ecosystem biophysical variables and carbon dioxide exchange, particularly in the Canadian Arctic. The results of this research also indicate high levels of functional convergence in ecosystem-level structure and function within Arctic landscapes. / Thesis (Ph.D, Geography) -- Queen's University, 2013-01-03 22:24:20.157