Agriculture and urban activities are major sources of phosphorus and nitrogen to aquatic ecosystems. Atmospheric deposition further contributes as a source of N. These nonpoint inputs of nutrients are difficult to measure and regulate because they derive from activities dispersed over wide areas of land and are variable in time due to effects of weather. In aquatic ecosystems, these nutrients cause diverse problems such as toxic algal blooms, loss of oxygen, fish kills, loss of biodiversity (including species important for commerce and recreation), loss of aquatic plant beds and coral reefs, and other problems. Nutrient enrichment seriously degrades aquatic ecosystems and impairs the use of water for drinking, industry, agriculture, recreation, and other purposes.

Based on our review of the scientific literature, we are certain that (1) eutrophication is a widespread problem in rivers, lakes, estuaries, and coastal oceans, caused by overenrichment with P and N; (2) nonpoint pollution, a major source of P and N to surface waters of the United States, results primarily from agriculture and urban activity, including industry; (3) inputs of P and N to agriculture in the form of fertilizers exceed outputs in produce in the United States and many other nations; (4) nutrient flows to aquatic ecosystems are directly related to animal stocking densities, and under high livestock densities, manure production exceeds the needs of crops to which the manure is applied; (5) excess fertilization and manure production cause a P surplus to accumulate in soil, some of which is transported to aquatic ecosystems; and (6) excess fertilization and manure production on agricultural lands create surplus N, which is mobile in many soils and often leaches to downstream aquatic ecosystems, and which can also volatilize to the atmosphere, redepositing elsewhere and eventually reaching aquatic ecosystems.

If current practices continue, nonpoint pollution of surface waters is virtually certain to increase in the future. Such an outcome is not inevitable, however, because a number of technologies, land use practices, and conservation measures are capable of decreasing the flow of nonpoint P and N into surface waters.

From our review of the available scientific information, we are confident that: (1) nonpoint pollution of surface waters with P and N could be reduced by reducing surplus nutrient flows in agricultural systems and processes, reducing agricultural and urban runoff by diverse methods, and reducing N emissions from fossil fuel burning; and (2) eutrophication can be reversed by decreasing input rates of P and N to aquatic ecosystems, but rates of recovery are highly variable among water bodies. Often, the eutrophic state is persistent, and recovery is slow.

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Nonpoint pollution of surface waters with phosphorus and nitrogen

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

The Soil and Water Assessment Tool (SWAT) model is a continuation of nearly 30 years of modeling efforts conducted by the USDA Agricultural Research Service (ARS). SWAT has gained international acceptance as a robust interdisciplinary watershed modeling tool as evidenced by international SWAT conferences, hundreds of SWAT-related papers presented at numerous other scientific meetings, and dozens of articles published in peer-reviewed journals. The model has also been adopted as part of the U.S. Environmental Protection Agency (USEPA) Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) software package and is being used by many U.S. federal and state agencies, including the USDA within the Conservation Effects Assessment Project (CEAP). At present, over 250 peer-reviewed published articles have been identified that report SWAT applications, reviews of SWAT components, or other research that includes SWAT. Many of these peer-reviewed articles are summarized here according to relevant application categories such as streamflow calibration and related hydrologic analyses, climate change impacts on hydrology, pollutant load assessments, comparisons with other models, and sensitivity analyses and calibration techniques. Strengths and weaknesses of the model are presented, and recommended research needs for SWAT are also provided.

/pdf/the-soil-and-water-assessment-tool-historical-development-4e4d97tdfq.pdf

The Soil and Water Assessment Tool: Historical Development, Applications, and Future Research Directions

The Soil and Water Assessment Tool (SWAT) model is a continuation of nearly 30 years of modeling efforts conducted by the U.S. Department of Agriculture (USDA), Agricultural Research Service. SWAT has gained international acceptance as a robust interdisciplinary watershed modeling tool, as evidenced by international SWAT conferences, hundreds of SWAT-related papers presented at numerous scientific meetings, and dozens of articles published in peer-reviewed journals. The model has also been adopted as part of the U.S. Environmental Protection Agency's BASINS (Better Assessment Science Integrating Point & Nonpoint Sources) software package and is being used by many U.S. federal and state agencies, including the USDA within the Conservation Effects Assessment Project. At present, over 250 peer-reviewed, published articles have been identified that report SWAT applications, reviews of SWAT components, or other research that includes SWAT. Many of these peer-reviewed articles are summarized here according to relevant application categories such as streamflow calibration and related hydrologic analyses, climate change impacts on hydrology, pollutant load assessments, comparisons with other models, and sensitivity analyses and calibration techniques. Strengths and weaknesses of the model are presented, and recommended research needs for SWAT are provided.

Soil and Water Assessment Tool: Historical Development, Applications, and Future Research Directions, The

Dormancy is a bet-hedging strategy used by a wide range of taxa, including microorganisms. It refers to an organism's ability to enter a reversible state of low metabolic activity when faced with unfavourable environmental conditions. Dormant microorganisms generate a seed bank, which comprises individuals that are capable of being resuscitated following environmental change. In this Review, we highlight mechanisms that have evolved in microorganisms to allow them to successfully enter and exit a dormant state, and discuss the implications of microbial seed banks for evolutionary dynamics, population persistence, maintenance of biodiversity, and the stability of ecosystem processes.

/pdf/microbial-seed-banks-the-ecological-and-evolutionary-1plh1l8co8.pdf

Microbial seed banks: the ecological and evolutionary implications of dormancy

The relationship between species diversity and ecosystem functioning has been debated for decades, especially in relation to the “macroscopic” realm (higher plants and metazoans). Although there is emerging consensus that diversity enhances productivity and stability in communities of higher organisms; however, we still do not know whether these relationships apply also for communities of unicellular organisms, such as phytoplankton, which contribute ≈50% to the global primary production. We show here that phytoplankton resource use, and thus carbon fixation, is directly linked to the diversity of phytoplankton communities. Datasets from freshwater and brackish habitats show that diversity is the best predictor for resource use efficiency of phytoplankton communities across considerable environmental gradients. Furthermore, we show that the diversity requirement for stable ecosystem functioning scales with the nutrient level (total phosphorus), as evidenced by the opposing effects of diversity (negative) and resource level (positive) on the variability of both resource use and community composition. Our analyses of large-scale observational data are consistent with experimental and model studies demonstrating causal effects of microbial diversity on functional properties at the system level. Our findings point at potential linkages between eutrophication and pollution-mediated loss of phytoplankton diversity. Factors reducing phytoplankton diversity may have direct detrimental effects on the amount and predictability of aquatic primary production.

https://www.pnas.org/content/pnas/105/13/5134.full.pdf

Diversity predicts stability and resource use efficiency in natural phytoplankton communities.

Phosphorus in agriculture and its environmental implications

The temporal changes and spatial variability of phosphorus andnitrogen losses and concentrations in Finland during the period1981–1997 were studied in 15 small agricultural and forestedcatchments In addition, four coastal river basins with highagricultural land use located in southern Finland were includedin the study in order to assess the representativeness ofagricultural loss estimates from small agricultural catchmentsThe mean annual loss specific for agricultural land was estimatedto be on average 110 kg km-2 a-1 for total phosphorusand 1500 kg km-2 a-1 for total nitrogen The resultsfrom small agricultural catchments were in agreement with thecorresponding loss estimates from rivers, with an average of137 kg km-2 a-1 for total phosphorus and 1800 kg km-2a-1 for total nitrogen The results from the studiedagricultural catchments and rivers during the period 1981–1997suggest that weather-driven fluctuation in discharge was usuallythe main reason for changes in nutrient losses, and little or noimpact of changes in agricultural production or managementpractises can be observed In forested areas the total phosphorusloss (average 9 kg km-2 a-1) and total nitrogen loss(average 250 kg km-2 a-1) were lower than inagricultural areas In forested catchments the impact of forestryoperations, such as clear-cutting and fertilization, and theimpact of atmospheric nitrogen deposition can be seen in changesin nutrient losses

Losses of Nitrogen and Phosphorus from Agricultural and Forest Areas in Finland during the 1980s and 1990s

The drastic loss of seminatural grasslands and the decrease in species diversity in Europe during the 20th century are closely linked to social-economic factors. Development in agricultural production drives land-use changes, and thus controls the capacity of landscapes to maintain biodiversity. In this study, we link agricultural production changes to landscape fragmentation and species diversity. Our results show that the termination of grazing on seminatural grassland caused significant changes in landscape structure and a decline in the number of vascular plant species. The decline of grazed grasslands has been driven mainly by farm-level economic efficiency and profitability interests, which have been connected with agricultural policy measures. Since 1995, when Finland joined the European Union, the area of grazed patches in our study area has again increased as a result of a support scheme for the management of seminatural grasslands.

Loss of plant species richness and habitat connectivity in grasslands associated with agricultural change in Finland.

Changes in climate, either long or short-term changes, can alter significantly the hydrological behavior of catchments. A statistical analysis of a thirty-four year time series of meteorological data collected in the Vantaanjoki watershed (Southern Finland) shows an increase in temperature and precipitation. The hydrological model SWAT was applied to the Vantaanjoki watershed in order to assess the impact of the measured transient climate change on the hydro-biogeochemical behavior of the catchment. The SWAT model was calibrated and validated for a period extending from 1965 to 1998. The model performance was evaluated comparing the measured and predicted time series for flow, suspended solids, total nitrogen and total phosphorus at the watershed outlet. The model was then run for the same period with climatic data where the observed increase in temperature and precipitation was removed using non-parametric techniques. It was shown that the observed climate change was responsible for the decrease of the snow cover and increase of winter runoff. On an annual basis, small increases were noted in nutrient losses, however, with significant seasonal differences. Globally, the observed climate change was responsible for an increased contribution of diffuse nutrient losses to the total nutrient load.

Seppo Rekolainen

Papers

Diversity predicts stability and resource use efficiency in natural phytoplankton communities.

Phosphorus in agriculture and its environmental implications

Losses of Nitrogen and Phosphorus from Agricultural and Forest Areas in Finland during the 1980s and 1990s

Loss of plant species richness and habitat connectivity in grasslands associated with agricultural change in Finland.

Impact of Climate Change on the Water Cycle and Nutrient Losses in a Finnish Catchment.