Decreasing Nutrient Loads Research Articles

Somatic growth of pikeperch (Stizostedion lucioperca) in relation to variation in temperature and eutrophication in a Central Europe Lake

Global climate change has been altering freshwater ecosystems by impacting many ecological processes, including individual fish growth. Predictions of responses of local fish populations to future environmental change can draw inferences from past long-term biochronological data. In this study, we reconstructed individual growth pattern of one of the most valuable predatory species in European inland waters, pikeperch (Stizostedion lucioperca), using back-calculated length from their otoliths. Samples were collected at the Lipno reservoir (Czech Republic) between 2008 and 2020. We used linear mixed-effects models to investigate how individual state and environmental conditions affect the somatic growth of the local pikeperch population. We found that individual growth rates increased with temperature and tended to be higher when chlorophyll-a concentration was higher, and water transparency was lower. This suggests the species will likely benefit from the warmer waters predicted in future climate scenarios. However, the decreasing nutrient loading associated with efforts to curb eutrophication in Central Europe may offset these benefits. Together, these results provide a better understanding of how multiple environmental factors, directly and indirectly, influence the somatic growth of pikeperch in long term.

Land Use and Climate Change Effects on Streamflow and Nutrient Loads in a Temperate Catchment: A Simulation Study

Climate and land use changes impact catchment hydrology and water quality (WQ), yet few studies have investigated the amount of land use changes required to meet specific WQ targets under future climate projections. The aim of this study was to determine streamflow and nutrient load responses to future land use change (LUC) and climate change scenarios. We hypothesized that (1) increasing forest coverage would decrease nutrient loads, (2) climate change, with higher temperatures and more intense storms, would lead to increased flow and nutrient loads, and (3) LUC could moderate potential nutrient load increases associated with climate change. We tested these hypotheses with the Soil and Water Assessment Tool (SWAT), which was applied to a lake catchment in New Zealand, where LUC strategies with afforestation are employed to address lake WQ objectives. The model was calibrated from 2002 to 2005 and validated from 2006 to 2010 using measured streamflow (Q) and total nitrogen (TN), total phosphorus (TP), nitrate (NO3-N), and ammonium (NH4-N) concentrations of three streams in the catchment. The model performance across the monitored streams was evaluated using coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE) metrics to provide a basis for model projections. Future scenarios incorporated LUC and climate change (CC) based on the Representative Concentration Pathway 8.5 and were compared to the baseline streamflow and WQ indicators. Consistent with our hypotheses, Q, TN, and TP loads were predicted to decrease with afforestation. Specifically, afforestation of 1.32 km2 in one of the monitored stream sub-catchments (subbasin 3), or 8.8% of the total lake catchment area, would result in reductions of 11.9, 26.2, and 17.7% in modeled annual mean Q, TN, and TP loads, respectively. Furthermore, when comparing simulations based on baseline and projected climate, reductions of 13.6, 22.8, and 19.5% were observed for Q, TN, and TP loads, respectively. Notably, the combined implementation of LUC and CC further decreased Q, TN, and TP loads by 20.2, 36.7, and 28.5%, respectively. This study provides valuable insights into the utilization of LUC strategies to mitigate nutrient loads in lakes facing water quality challenges, and our findings could serve as a prototype for other lake catchments undergoing LUC. Contrary to our initial hypotheses, we found that higher precipitation and temperatures did not result in increased flow and nutrient loading.

Deciphering large-scale spatial pattern and modulators of dissolved greenhouse gases (CO2, CH4, and N2O) along the Yangtze River, China

The Yangtze River, the third largest river around the globe, has been heavily engineered with a series of hydroelectric dams. Meanwhile, it receives elevated organic matter and nutrient loads from its densely populated catchment, subsequently altering dissolved greenhouse gas (GHG) concentrations along the river. However, the large-scale longitudinal patterns and drivers of GHG concentrations in the Yangtze River remain poorly understood. Using longitudinal sampling design in a 2400 km section, we report dissolved carbon dioxide, methane, and nitrous oxide concentrations along the Yangtze River at 145 sites. We observe significant spatial clustering with higher carbon dioxide and nitrous oxide concentrations in the middle reach of the Yangtze River. The results of nonlinear regression reveal that riverine GHGs are high when wetland coverage is high and dissolved oxygen is low. Wetlands and oxygen, not the Three Gorges Dam and tributaries, are the primary correlates of spatial variations of CO2 and CH4 concentrations, respectively. N2O is surprisingly well predicted by CO2, implying their common drivers or sources. We strongly recommend that wetland contribution to GHG budgets and its sensitivity to environmental change be considered when estimating riverine GHGs in the Yangtze River. In light of our study, future control of GHG emissions from large rivers may largely depend on how external inputs and internal metabolism are regulated by decreasing nutrient loading.

Status, Trends, and Drivers of Harmful Algal Blooms Along the Freshwater-to-Marine Gradient in the San Francisco Bay–Delta System

Harmful algal blooms (HABs) are on the rise worldwide. Known drivers for the proliferation and intensification of HAB events include increasing nutrient pollution, climate change, regulation and modification of hydrological flow, and the combined effect of climate drivers and nutrient pollution. The San Francisco Bay–Delta system has largely been immune to severe or acute HAB events, but there is both a potential and realized threat which has been underestimated and under-reported, in part because of the lack of coordinated sampling and data reporting. There is also increasing evidence that HABs must be considered in the context of a freshwater-to-marine continuum, and that the physical and political boundaries separating components of the Bay–Delta system are porous barriers to HABs and their toxins. Much remains to be learned about the ecology and physiology of HAB organisms in this system, but five primary environmental drivers can be identified: temperature, salinity, irradiance, nutrients, and stratification/residence time. All these drivers are responding rapidly to climate change, but nutrients are the primary variable that is largely under human control. Plans for the development of a comprehensive monitoring, prediction, and mitigation strategy across the freshwater-to-marine continuum have been documented; effectively following through on these plans provides a roadmap toward identifying the drivers and threats—and reducing the potential consequences now and in the future. While HABs alone are not a sufficient motivator for potentially costly and extensive mitigation efforts, there is strong evidence that decreasing nutrient loads, maintaining hydrological connectivity while minimizing stagnant regions, and managing the biota to maintain biodiversity of the Bay–Delta system will result in multiple co-benefits, including reduction of the HAB threat potential.

Transitioning from conventional to cover crop systems with minimum tillage does not alter nutrient loading.

Nutrient loading from conventional row-crop production systems impairs surface waterbodies in the mid-southern United States. This study was conducted to determine whether minimum tillage and winter cover crops can decrease nutrient loading in surface runoff from conventionally tilled row-crop fields. The effects of winter cover crops and minimum tillage on N and P loading from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation system were investigated on production fields in northwestern Mississippi using a split-field approach. As measured at the edge of the field, minimum tillage with cover crops had no effect on surface runoff from production fields regarding N or P loading (p >.10 for all nutrient loads), discharge (p >.10), or loss of suspended solids (p >.10). Minimum tillage and cover crops decreased sediment and nutrient concentrations in runoff for total N (p =.05) and total P (p =.09) but had no effect on other nutrients of interest. Although these practices decreased total N concentration by 36% in surface runoff to receiving waters, this reduction was only seen when aboveground cover crop biomass was present (p =.07). Regardless of the time of year, minimum tillage with cover crops decreased total P concentration in surface runoff by 27% (p=.09). These data indicate that it is unlikely that minimum tillage and cover crops will affect N and P loading while transitioning to a conservation production system in the mid-southern United States.

Adoption and perception of cover crop implementation for tropical fruit growers

Cover cropping is a sustainable strategy for increasing soil nutrients and organic matter, and improving overall soil health. This practice is heavily promoted for annual vegetable growers; however, there is less widespread acknowledgement for cover crops as a management strategy in perennial settings. Research is limited in this field, specifically when considering cover cropping for tropical fruit groves. The current study analyzes data from surveys distributed to Miami-Dade County (MDC) tropical fruit producers to quantify their perceptions on incorporating cover crops in their fruit production systems. Two surveys were formulated and distributed virtually to understand farmer familiarity/interest in cover cropping and to uncover factors that impact likelihood of cover crop adoption. Logistic regression analysis of cover crop adoption revealed that having previous experience with cover crops, valuing cover crop importance, perceiving the practice as economically viable, and farm acreage were all positive predictors of cover crop adoption. When questioned about specific tropical leguminous cover crop species, sunn hemp (<i>Crotalaria juncea</i> L.) and velvet bean (<i>Mucuna pruriens</i> [L.] DC), farmers expressed ~5% greater interest in incorporating sunn hemp into their production systems. Quantitative and qualitative data revealed that 90% of surveyed farmers were interested in learning more about cover crops and 85% were likely to attend demonstrative workshops to discern if implementing cover crops would be right for their operation. Overall, the findings suggest that MDC fruit producers are interested in incorporating cover cropping practices with 80% of respondents indicating they would like to improve conservation practices within their production systems. Applying cover crops can potentially improve soil quality and reduce erosion in the MDC agricultural area and in other regions where perennial fruit crop production is prominent. Additionally, implementation of cover cropping as a substitute to reduce usage of synthetic fertilizers has positive implications to decrease nutrient loads in the imperiled ecosystems of Florida Bay and the Everglades.

Evaluating management options to reduce Lake Erie algal blooms using an ensemble of watershed models

Reducing harmful algal blooms in Lake Erie, situated between the United States and Canada, requires implementing best management practices to decrease nutrient loading from upstream sources. Bi-national water quality targets have been set for total and dissolved phosphorus loads, with the ultimate goal of reaching these targets in 9-out-of-10 years. Row crop agriculture dominates the land use in the Western Lake Erie Basin thus requiring efforts to mitigate nutrient loads from agricultural systems. To determine the types and extent of agricultural management practices needed to reach the water quality goals, we used five independently developed Soil and Water Assessment Tool models to evaluate the effects of 18 management scenarios over a 10-year period on nutrient export. Guidance from a stakeholder group was provided throughout the project, and resulted in improved data, development of realistic scenarios, and expanded outreach. Subsurface placement of phosphorus fertilizers, cover crops, riparian buffers, and wetlands were among the most effective management options. But, only in one realistic scenario did a majority (3/5) of the models predict that the total phosphorus loading target would be met in 9-out-of-10 years. Further, the dissolved phosphorus loading target was predicted to meet the 9-out-of-10-year goal by only one model and only in three scenarios. In all scenarios evaluated, the 9-out-of-10-year goal was not met based on the average of model predictions. Ensemble modeling revealed general agreement about the effects of several practices although some scenarios resulted in a wide range of uncertainty. Overall, our results demonstrate that there are multiple pathways to approach the established water quality goals, but greater adoption rates of practices than those tested here will likely be needed to attain the management targets.

Recovery of a Tidal Freshwater Embayment from Eutrophication: a Multidecadal Study

Effective management of eutrophication in tidal ecosystems requires a thorough understanding of the dynamics of their responses to decreases in nutrient loading. We analyze a 34-year dataset on a shallow embayment of the tidal freshwater Potomac River, Gunston Cove, for long-term responses of ambient nutrient levels, light transparency measures, phytoplankton biomass, and coverage of submersed aquatic vegetation (SAV) to decreased nutrient loading. Point source loading of phosphorus, the nutrient most limiting primary production in this system, was greatly curtailed coincident with the study onset (1983/84) exhibiting a sharp decrease of 95% from peak loading levels. However, water column total phosphorus decreased much more slowly and gradually. Phytoplankton chlorophyll a did not show a distinctive decrease until 2000 and SAV responded strongly beginning in 2004. The habitat suitability model for SAV developed by Chesapeake Bay researchers was able to explain the recovery of SAV coverage based on data on light transparency and basin morphometry collected in this study. The study results were consistent with the alternative stable state theory with a sharp transition from a phytoplankton-dominated “turbid water” state to an SAV-dominated “clear water” state in a 2-year period from 2003 to 2005. The system eventually responded to nutrient load reductions, but the nonlinear and incomplete nature of this recovery and the two-decade delay illustrate the complexities of managing these systems.

The meagre future of benthic fauna in a coastal sea-Benthic responses to recovery from eutrophication in a changing climate.

Nutrient loading and climate change affect coastal ecosystems worldwide. Unravelling the combined effects of these pressures on benthic macrofauna is essential for understanding the future functioning of coastal ecosystems, as it is an important component linking the benthic and pelagic realms. In this study, we extended an existing model of benthic macrofauna coupled with a physical-biogeochemical model of the Baltic Sea to study the combined effects of changing nutrient loads and climate on biomass and metabolism of benthic macrofauna historically and in scenarios for the future. Based on a statistical comparison with a large validation dataset of measured biomasses, the model showed good or reasonable performance across the different basins and depth strata in the model area. In scenarios with decreasing nutrient loads according to the Baltic Sea Action Plan but also with continued recent loads (mean loads 2012-2014), overall macrofaunal biomass and carbon processing were projected to decrease significantly by the end of the century despite improved oxygen conditions at the seafloor. Climate change led to intensified pelagic recycling of primary production and reduced export of particulate organic carbon to the seafloor with negative effects on macrofaunal biomass. In the high nutrient load scenario, representing the highest recorded historical loads, climate change counteracted the effects of increased productivity leading to a hyperbolic response: biomass and carbon processing increased up to mid-21st century but then decreased, giving almost no net change by the end of the 21st century compared to present. The study shows that benthic responses to environmental change are nonlinear and partly decoupled from pelagic responses and indicates that benthic-pelagic coupling might be weaker in a warmer and less eutrophic sea.

An ecological scenario prediction model for newly created wetlands caused by coal mine subsidence in the Yanzhou, China.

The ecological model we developed can simulate the state of wetlands and predict ecosystem development by varying both parameter settings and forcing functions. The newly created wetland resulting from large-scale coal mining is a distinct type of wetland, but existing ecological models for this wetland type are limited in number and scope. The Yanzhou coalfield, located in Shandong Province in China, contains a typical newly created wetland that came into being after coal mining subsidence. We developed an ecological model for this wetland that estimates values for four state variables: phytoplankton biomass (A), zooplankton biomass (Z), sediment biomass (D), and hydrophyte biomass (H). Analysis of the results showed that the model was sensitive to changes in nutrient loading. As nutrient loads increased, plankton biomass increased, and the ratio of zooplankton biomass to phytoplankton biomass (Z/A) decreased. We defined three prediction scenarios for the wetland and calculated their eco-exergies to compare the ecological effects for each scenario. The most effective measures to improve the state of the ecosystem are to reduce the subsidence depth and to decrease nutrient loading.

Impact of land use change on multiple ecosystem services in the rapidly urbanizing Kunshan City of China: Past trajectories and future projections

Formulation of suitable land use strategies for sustainable management of urban landscapes requires assessment of the potential impact of future urban expansion on ecosystem services. We assessed land use change in the rapidly urbanizing Kunshan City of China during 2006–2016 and projected future land uses in 2030 under three alternative scenarios: Business-As-Usual (BAU), Croplands Protection (CP), and Ecological Restoration (ER). Then we quantified the spatio-temporal variations of six ecosystem services (including crop production, carbon storage, habitat quality, flood regulation, and nitrogen and phosphorus retention) in response to urban land use change from 2006 to 2030 using the InVEST model. We also analyzed temporal variation of the tradeoffs and synergies among multiple ecosystem services throughout the period of study. Our estimates indicate that the urban land of Kunshan increased by 19% over the past decade and will continue to expand by 15% from 2016 to 2030 under the BAU scenario. As a result, crop production, carbon storage, habitat quality, and flood regulation capacity would all decrease tremendously. Crop production would remain stable under the CP scenario owing to the strict protection of croplands, but nitrogen and phosphorus loading would increase by 8%. In contrast, the ER scenario would decrease nutrient loading by over 35% with concomitant benefits to carbon storage, habitat quality, and flood regulation capacity. However, crop production would decrease dramatically under the ER scenario, primarily due to the transition of large areas of croplands to ecological zones. Although croplands were the major sources for nitrogen and phosphorus loading in Kunshan during the years 2006–2016, urban land would become the major source of pollution under all future scenarios. Crop production and habitat quality were not significantly correlated during the years 2006–2016, while they would be positively correlated under the BAU and CP scenarios. This implies that croplands would become increasingly important in providing habitats as urban land continues to expand by replacing ecological land from 2016 to 2030. We propose four major land use strategies, including compact urban growth, croplands protection, reforestation to build greenways, and wetlands restoration in the riparian areas of drinking water sources to improve ecosystem services in Kunshan.

Identifying multiple stressors that influence eutrophication in a Finnish agricultural river

In Finland, a recent ecological classification of surface waters showed that the rivers and coastal waters need attention to improve their ecological state. We combined eco-hydrological and empirical models to study chlorophyll-a concentration as an indicator of eutrophication in a small agricultural river. We used a modified story-and-simulation method to build three storylines for possible changes in future land use due to climate change and political change. The main objective in the first storyline is to stimulate economic activity but also to promote the sustainable and efficient use of resources. The second storyline is based on the high awareness but poor regulation of environmental protection, and the third is to survive as individual countries instead of being part of a unified Europe. We assumed trade of agricultural products to increase to countries outside Europe. We found that chlorophyll-a concentration in the river depended on total phosphorus concentration. In addition, there was a positive synergistic interaction between total phosphorus and water temperature. In future storylines, chlorophyll-a concentration increased due to land use and climate change. Climate change mainly had an indirect influence via increasing nutrient losses from intensified agriculture. We found that well-designed agri-environmental measures had the potential to decrease nutrient loading from fields, as long as the predicted increase in temperature remained under 2 °C. However, we were not able to achieve the nutrient reduction stated in current water protection targets. In addition, the ecological status of the river deteriorated. The influence of temperature on chlorophyll-a growth indicates that novel measures for shading rivers to decrease water temperature may be needed in the future.

Recent trends in nutrient and sediment loading to coastal areas of the conterminous U.S.: Insights and global context

Coastal areas in the U.S. and worldwide have experienced massive population and land-use changes contributing to significant degradation of coastal ecosystems. Excess nutrient pollution causes coastal ecosystem degradation, and both regulatory and management efforts have targeted reducing nutrient and sediment loading to coastal rivers. Decadal trends in flow-normalized nutrient and sediment loads were determined for 95 monitoring locations on 88 U.S. coastal rivers, including tributaries of the Great Lakes, between 2002 and 2012 for nitrogen (N), phosphorus (P), and sediment. N and P loading from urban watersheds generally decreased between 2002 and 2012. In contrast, N and P trends in agricultural watersheds were variable indicating uneven progress in decreasing nutrient loading. Coherent decreases in N loading from agricultural watersheds occurred in the Lake Erie basin, but limited benefit is expected from these changes because P is the primary driver of degradation in the lake. Nutrient loading from undeveloped watersheds was low, but increased between 2002 and 2012, possibly indicating degradation of coastal watersheds that are minimally affected by human activities. Regional differences in trends were evident, with stable nutrient loads from the Mississippi River to the Gulf of Mexico, but commonly decreasing N loads and increasing P loads in Chesapeake Bay. Compared to global rivers, coastal rivers of the conterminous U.S have somewhat lower TN yields and slightly higher TP yields, but similarities exist among land use, nutrient sources, and changes in nutrient loads. Despite widespread decreases in N loading in coastal watersheds, recent N:P ratios remained elevated compared to historic values in many areas. Additional progress in reducing N and P loading to U.S. coastal waters, particularly outside of urban areas, would benefit coastal ecosystems.

Silage storage runoff characterization: Annual nutrient loading rate and first flush analysis of bunker silos

Bunker silos produce a runoff that is a source of nutrient loss and a threat to surface water quality. Little information is available on the water quality of stormwater produced from bunker silos. This research evaluated the runoff characteristics from six horizontal bunker facilities at dairy farms to determine runoff water quality and nutrient loading throughout a storm and annual nutrient losses. On average, at 50% of the cumulative runoff volume the difference between cumulative nutrient load and volume did not exceed 20%, which is a threshold required for a first flush scenario (cumulative loads of P and N were 1.5 to 4.5% and −2.8 to 4.0% greater than cumulative volume, respectively). During the storage of silage in horizontal bunker silos an estimated 0.3 to 1.8% of ensiled P and 0.4 to 1.7% of ensiled N was lost annually with silage runoff. Assessment of a theoretical dairy farm in WI has a calculated runoff loss from horizontal feed storage of 30% and 55% of the total farmstead N and P runoff losses, respectively. Nitrogen (N) and phosphorus (P) loading from bunker silos were relatively consistent throughout a storm with no evidence of a first flush scenario. Annual variability in low flow N and P concentrations were impacted by the production of silage leachate, and bunkers with subsurface collection reduced the nutrient concentrations in overflow runoff. Dairy bunkers provide an opportunity to decrease nutrient loading, through management of a small land base, as compared to other farmstead runoff areas. Reducing the amount of silage runoff lost from dairy farms has strong potential for N and P conservation.

Abiotic and biotic controls of phytoplankton biomass dynamics in a freshwater tributary, estuary, and large lake ecosystem: Sandusky Bay (Lake Erie) chemostat

The classic view of tributary–lake interactions solely considers tributaries as sources of nutrients for phytoplankton growing offshore. We tested how river input of phytoplankton affected dynamics in a lacustrine estuary and how these phytoplankters could, upon discharge, affect offshore phytoplankton dynamics. In addition, we explored whether phytoplankton biomass was controlled by bottom-up abiotic factors (stream flow, temperature, light attenuation, and nutrient concentrations) or top-down biotic factors (zooplankton herbivory) and the role the lacustrine estuary played in modifying the quality of the water discharged into the lake. We tested these possibilities using field sampling over 2 years in the Sandusky River, Sandusky Bay, and the Sandusky subbasin of Lake Erie in conjunction with river flow and nutrient monitoring and multivariate statistical analysis of the relationships among the various datasets. Nutrient loading to the estuary corresponded with watershed input; nutrients were used within the estuary, decreasing nutrient loads to the lake. Phytoplankton biomass, however, was extremely high in the estuary and was much higher at the bay–subbasin interface than offshore, indicating that the estuary likely discharges phytoplankton to the nearshore area, not offshore. An information-theoretic analysis of 15 candidate models showed that phytoplankton biomass was best predicted by the ratio of total inorganic nitrogen to total phosphorus, indicating bottom-up control. The lacustrine estuary therefore functions as a chemostat, using incoming nutrients to grow large amounts of phytoplankton. Our results indicate that the classic model of tributary–bay interactions needs revision to include phytoplankton load and its subsequent effects within the lake.

Long-term changes in the fish community structure revealed by gillnet monitoring in a shallow, lowland reservoir

Background. Fish communities can support or hinder water quality management. Sulej&oacute;w Reservoir, which is situated on the Pilica River in Central Poland, serves as a strategic reserve of drinking water for the &#321;&oacute;d&#378; Agglomeration. Precise knowledge of the long-term dynamics of the structure of the fish community, what was the aim of this study, is important for proper management to slow the eutrophication of the reservoir and prevent toxic algal blooms. Materials and methods. To determine fish species composition, multimesh gill nets with mesh sizes ranging from 11 to 80 mm were used. From 1993 to 2015, gillnetting was conducted 1&ndash;2 times per month from June through November in two representative parts of the reservoir, and principal component analysis (PCA) was applied to explore the temporal variation in fish community structure expressed as the relative contribution of each species to the total fish biomass. Results. Dominance fluctuated among four species in the fish community: common bream, Abramis brama (Linnaeus, 1758); roach, Rutilus rutilus (Linnaeus, 1758); white bream, Blicca bjoerkna (Linnaeus, 1758); and pike-perch, Sander lucioperca (Linnaeus, 1758). PCA revealed three principal components with eigenvalues larger than one that explained 73.3% of the observed variance in the temporal changes in fish community composition. A negative correlation was found between pike-perch biomass and roach biomass (r = 0.82), while a positive correlation was observed between the biomass of pike-perch and that of common bream (r = 0.73). Consequently, there was a highly negative correlation between the biomasses of common bream and roach (r = 0.80). Furthermore, an interesting temporal pattern was observed; from 1993 to 2000, the fish community was dominated by common bream and pike-perch but then shifted towards domination by roach and white bream, despite declining phosphorous and carbon concentrations. Recently, this trend has been reversed, and a more balanced fish community structure has been established. Conclusion. Fish community succession, which is usually reported to be a one-directional process in reservoirs, i.e., from a riverine fish or percid-dominated to a cyprinid (bream)-dominated state, was more ambiguous in Sulej&oacute;w Reservoir. This was likely a consequence of both restoration issues related to decreasing nutrient loads and the influence of zebra mussel, Dreissena polymorpha invasion on the trophic relations in the reservoir.

Controls on methane concentrations and fluxes in streams draining human-dominated landscapes.

Streams and rivers are active processors of carbon, leading to significant emissions of CO2 and possibly CH4 to the atmosphere. Patterns and controls of CH4 in fluvial ecosystems remain relatively poorly understood. Furthermore, little is known regarding how major human impacts to fluvial ecosystems may be transforming their role as CH4 producers and emitters. Here, we examine the consequences of two distinct ecosystem changes as a result of human land use: increased nutrient loading (primarily as nitrate), and increased sediment loading and deposition of fine particles in the benthic zone. We did not find support for the hypothesis that enhanced nitrate loading down-regulates methane production via thermodynamic or toxic effects. We did find strong evidence that increased sedimentation and enhanced organic matter content of the benthos lead to greater methane production (diffusive + ebullitive flux) relative to pristine fluvial systems in northern Wisconsin (upper Midwest, USA). Overall, streams in a human-dominated landscape of southern Wisconsin were major regional sources of CH4 to the atmosphere, equivalent to ~20% of dairy cattle emissions, or ~50% of a landfill's annual emissions. We suggest that restoration of the benthic environment (reduced fine deposits) could lead to reduced CH4 emissions, while decreasing nutrient loading is likely to have limited impacts to this ecosystem process.

Biological indicators track differential responses of pelagic and littoral areas to nutrient load reductions in German lakes

External nutrient loading was reduced over the past decades as a measure for improving the water quality of eutrophic lakes in western Europe, and has since been accelerated by the adoption of the European Water Framework Directive (WFD) in 2000 (EC, 2000). A variety of eutrophication-related metrics have indicated that the response of biological communities to this decreased nutrient loading has been diverse. Phytoplankton, a major component of the pelagic community, often responded rapidly, whereas a significant delay was observed for submerged macrophytes colonizing littoral areas. In this study we tested whether assessment methods developed for phytoplankton and macrophytes in lakes during Germany's implementation of the WFD reflect this differential response. An assessment of 263 German lakes confirmed that a lower ecological state was recorded when based on the biological quality element (BQE) for macrophytes than the BQE for phytoplankton during the investigated period (2003–2012). On average, lakes had a moderate ecological status for both phytoplankton and macrophyte BQEs, but differences of up to three classes were observed in single cases. Long-term data were available for five lowland lakes subject to strong reductions in phosphorus loading. Their phytoplankton-based assessments indicated a constant improvement of the ecological status in parallel to decreasing water phosphorus concentrations. In contrast, macrophyte-based assessments indicated a 10–20 year delay in their ecological recovery following nutrient load reduction. This delay was confirmed by detailed data on the temporal development of macrophyte species diversity and maximum colonization depths of two lakes after nutrient load reduction. We conclude that the available WFD assessment methods for phytoplankton and macrophyte BQEs are suitable to track the differential response of pelagic and littoral areas to nutrient load reductions in German lakes.

Accelerated water quality improvement during oligotrophication in peri-alpine lakes.

Monitoring of four eutrophic Swiss lakes undergoing oligotrophication during more than 25 years (i.e., gradually decreasing nutrient loading, productivity, and associated symptoms of eutrophication) revealed that phosphorus (P) net sedimentation rates (the fraction of a lake's total P content that is buried within its sediments each year) and P export rates (the fraction of the lakes' total P content that is exported via the outlet each year) increased as the lakes' P contents decreased. These findings are of scientific as well as practical interest because they imply that, contrary to the hitherto prevailing view, the P concentration of eutrophic lakes will decrease more than proportional to the reduction of their external P load, and faster than predicted by the linear (eutrophic state-based) models.

Nutrient Concentrations in a Pampasic First Order Stream with Different Land Uses in the Surrounding Plots (Buenos Aires, Argentina)

The objective of this study was to assess the effect of land use on nutrient concentrations in a Pampasic stream. Soluble reactive phosphorus (SRP) concentrations in the stream were higher at a site surrounded by fertilized double-cropped wheat/soybeans than at unfertilized soybeans plots. Nitrate and SRP concentrations in the stream were lower at sites surrounded by soybeans than livestock. It is suggested that crop fertilization and cattle manure increased nutrients loads released to the stream. It is suggested that preservation and restoration of riparian habitats may benefit water quality by decreasing nutrient loads.