Excessive Nutrient Loading Research Articles

Impact of accelerated future global mean sea level rise on hypoxia in the Baltic Sea

Expanding hypoxia is today a major threat for many coastal seas around the world and disentangling its drivers is a large challenge for interdisciplinary research. Using a coupled physical-biogeochemical model we estimate the impact of past and accelerated future global mean sea level rise (GSLR) upon water exchange and oxygen conditions in a semi-enclosed, shallow sea. As a study site, the Baltic Sea was chosen that suffers today from eutrophication and from dead bottom zones due to (1) excessive nutrient loads from land, (2) limited water exchange with the world ocean and (3) perhaps other drivers like global warming. We show from model simulations for the period 1850–2008 that the impacts of past GSLR on the marine ecosystem were relatively small. If we assume for the end of the twenty-first century a GSLR of +0.5 m relative to today’s mean sea level, the impact on the marine ecosystem may still be small. Such a GSLR corresponds approximately to the projected ensemble-mean value reported by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. However, we conclude that GSLR should be considered in future high-end projections (>+1 m) for the Baltic Sea and other coastal seas with similar hydrographical conditions as in the Baltic because GSLR may lead to reinforced saltwater inflows causing higher salinity and increased vertical stratification compared to present-day conditions. Contrary to intuition, reinforced ventilation of the deep water does not lead to overall improved oxygen conditions but causes instead expanded dead bottom areas accompanied with increased internal phosphorus loads from the sediments and increased risk for cyanobacteria blooms.

Sustainable fisheries in shallow lakes: an independent empirical test of the Chinese mitten crab yield model

Next to excessive nutrient loading, intensive aquaculture is one of the major anthropogenic impacts threatening lake ecosystems. In China, particularly in the shallow lakes of mid-lower Changjiang (Yangtze) River, continuous overstocking of the Chinese mitten crab (Eriocheir sinensis) could deteriorate water quality and exhaust natural resources. A series of crab yield models and a general optimum-stocking rate model have been established, which seek to benefit both crab culture and the environment. In this research, independent investigations were carried out to evaluate the crab yield models and modify the optimum-stocking model. Low percentage errors (average 47%, median 36%) between observed and calculated crab yields were obtained. Specific values were defined for adult crab body mass (135 g/ind.) and recapture rate (18% and 30% in lakes with submerged macrophyte biomass above and below 1 000 g/m2) to modify the optimum-stocking model. Analysis based on the modified optimum-stocking model indicated that the actual stocking rates in most lakes were much higher than the calculated optimum-stocking rates. This implies that, for most lakes, the current stocking rates should be greatly reduced to maintain healthy lake ecosystems.

Pre-development conditions to assess the impact of growth in an urbanizing watershed in Northern Virginia

Pre-development conditions are an easily understood state to which watershed nonpoint nutrient reduction targets may be referenced. Using the pre-development baseline, a “developed-excess” measure may be computed for changes due to anthropogenic development. Developed-excess is independent of many geographical, physical, and hydrological characteristics of the region and after normalization by area may be used for comparison among various sub-sets of the watershed, such as jurisdictions or land use types. We have demonstrated this method by computing pre-development nitrogen and phosphorus loads entering the Occoquan Reservoir from its tributary watershed in Northern Virginia. The pre-development loads in this study were computed using the calibrated water quality models for the period 2002–2007. Current forest land was used as a surrogate for pre-development land use conditions for the watershed and developed-excess was estimated for fluvial loads of Total Inorganic Nitrogen (TIN) and Orthophosphate-Phosphorus (OP) by subtracting simulated predevelopment loads from observed loads. It was observed that within the study period (2002–2007), the average annual developed-excess represented about 30% of the TIN and OP average annual loads exported to the reservoir. Comparison of the two disturbed land use types, urban and agricultural, showed that urban land uses exported significantly more excess nonpoint nutrient load per unit area than agricultural land uses.

Environmental assessment of drainage water impacts on water quality and eutrophication level of Lake Idku, Egypt

Lake Idku, northern Egypt, receives large quantities of drainage water from four main discharging drains. Ecological and biological status of Lake Idku has been monitored during (autumn 2012 to summer 2013) to examine the lake water quality and eutrophication level in response to the quality as well as the source of the discharging water. Discrete water samples were collected from the lake body and the drains. Chemical analyses revealed an excessive nutrient load goes into the lake. A range of 1.4–10.6 mg nitrites/L was determined for drain waters, however a sudden increase was observed in lake and drain water samples of up to 84 and 74.5 mg/L, respectively. Reactive silicate ranged between 2.9 and 4.8 mg/L; while inorganic phosphate fluctuated between 0.2 and 0.43 mg/L. Transparency varied from 45 cm to 134 cm with better light conditions at drain sites. Biological results indicated a hyper-eutrophic status for the lake with a range of chlorophyll-a varied from a minimum of 39.9 μg/L (at Idku Drains) and a maximum of 104.2 μg/L (at El-Khairy drain). Phytoplankton community structure revealed higher abundance at lake sites compared with the drains. Maximum phytoplankton density was detected during summer with the dominance of Bacilariophyceae (e.g. Cyclotella meneghiniana, Cyclotella comate, Melosira varians) followed by Chlorophycean taxon (e.g. Scenedesmus dimorphus, S. bijuga and Crucigenia tetrapedia). Five indices were applied to evaluate the water quality of the lake. Diversity Index (DI) indicated slight to light pollution along all sites; while Sapropic Index (SI) indicated slight pollution with acceptable oxygen conditions and an availability of sensitive species. Palmer Index (PI) gave a strong evidence of high organic pollution at some sites in the lake, while Generic Diatom Index (GDI) revealed that levels of pollution varied from average to strong. Trophic Index (TI), suggest that there are an obvious signs of eutrophication in the lake.

Bases limnologicas para la gestion de los lagos urbanos de Concepcion, Chile

Morphological, physical and chemical characteristics of urban lakes of Conception were studied. The results indicate that these lakes are in an advanced process of eutrophication caused by excessive anthropogenic nutrient loads (mainly phosphorus and nitrogen). Furthermore, high concentrations of faecal and total coliforms in the water column and heavy metals in the sediments of these lakes were recorded. The principal component analyses showed that total phosphorus, ammonia, pH, conductivity, transparency and chlorophylla, are the variables that best explain the water conditions of all the lakes studied. It is recommended to orientate the lake management actions to decrease total phosphorus. Considering the particular situation of each lake, a series of complementary measures for reversing the current situation should be applied. This study provides new limnological information for the decision-making process focussed on the recovery of urban lakes of the City of Concepcion.

Palmitate-induced changes in energy demand cause reallocation of ATP supply in rat and human skeletal muscle cells

Mitochondrial dysfunction has been associated with obesity-related muscle insulin resistance, but the causality of this association is controversial. The notion that mitochondrial oxidative capacity may be insufficient to deal appropriately with excessive nutrient loads is for example disputed. Effective mitochondrial capacity is indirectly, but largely determined by ATP-consuming processes because skeletal muscle energy metabolism is mostly controlled by ATP demand. Probing the bioenergetics of rat and human myoblasts in real time we show here that the saturated fatty acid palmitate lowers the rate and coupling efficiency of oxidative phosphorylation under conditions it causes insulin resistance. Stearate affects the bioenergetic parameters similarly, whereas oleate and linoleate tend to decrease the rate but not the efficiency of ATP synthesis. Importantly, we reveal that palmitate influences how oxidative ATP supply is used to fuel ATP-consuming processes. Direct measurement of newly made protein demonstrates that palmitate lowers the rate of de novo protein synthesis by more than 30%. The anticipated decrease of energy demand linked to protein synthesis is confirmed by attenuated cycloheximide-sensitivity of mitochondrial respiratory activity used to make ATP. This indirect measure of ATP turnover indicates that palmitate lowers ATP supply reserved for protein synthesis by at least 40%. This decrease is also provoked by stearate, oleate and linoleate, albeit to a lesser extent. Moreover, palmitate lowers ATP supply for sodium pump activity by 60–70% and, in human cells, decreases ATP supply for DNA/RNA synthesis by almost three-quarters. These novel fatty acid effects on energy expenditure inform the ‘mitochondrial insufficiency’ debate.

Regional self-reliance for livestock feed, meat, dairy and eggs in the Northeast USA

AbstractThe production of livestock feed in the USA is geographically concentrated, which poses several risks. Extreme weather events and disease outbreaks have the potential to disrupt production in these areas, which could reduce the national output of meat, dairy and eggs. Additionally, geographically concentrated livestock and feed production systems have been observed to contribute excessive nutrient loads to surrounding soil and water bodies, thereby threatening environmental sustainability. Geographic relocation of production systems has been proposed as an adaptation strategy to increase system resilience and this could take the shape of more geographically dispersed livestock feed production. We estimate the degree to which the demand for meat, dairy and eggs in the Northeast region is met with current levels of regional feed and livestock production, a term that we refer to as regional self-reliance. We combine mean annual (2001–2010) data on Northeast regional land use; crop output; meat, dairy and egg output; and food consumption with a livestock feed requirements model. An annual mean of over 6.1 million ha of land in the Northeast was dedicated to livestock feed from 2001 to 2010, with nearly 80% located in just three states (Pennsylvania, New York and West Virginia). The region is a net importer of livestock feed (in terms of total digestible nutrients and crude protein), as well as meat, dairy and eggs (in terms of total human-edible energy and protein). This is the result of a confluence of long-term regional trends that include the movement of agricultural production out of the region with a concomitant increase in the regional population and an increase in the national demand for meat, dairy and eggs. Limited slaughter output in the region is a key limiting factor to increasing the region's self-reliance for livestock products.

Spotlight on Sediments: How is the Chesapeake Bay affected by storm flows from the Conowingo Reservoir?

Spotlight on Sediments: How is the Chesapeake Bay affected by storm flows from the Conowingo Reservoir?

Adaptive Capacity for eutrophication governance of the Laurentian Great Lakes

IntroductionEutrophication refers to the nutrient over-enrichment of water bodies and is one manifestation of anthropogenic adverse impact on the environment worldwide (Smith, 2003). The interactive world map on the World Resources Institute Website (World Resources Institute, 2015) vividly showcases examples of eutrophic water bodies worldwide, including Lake Erie in Canada and the United States, the Susquehanna River in the United States, Lake Winnipeg in Canada and the Bohai Sea in China. Lake Erie has been subject to severe eutrophication in the 20th century, with excessive nutrient loading in the 1960s and 1970s. Indeed, it was primarily eutrophication that prompted the US and Canada to sign the Great Lakes Water Quality Agreement (GLWQA) in 1972, with stipulated nutrient loading reduction targets for the lake. These phosphorus (P) loadings were from both point (sewage treatment plants, industrial discharges) and non-point sources (agriculture, urban runoff), but measures in the GLWQA focused on point source reduction through phosphorus control technologies and regulations for phosphorus in detergents and sewage treatment effluents (DePinto et al., 1986). Whilst these measures were successful and resulted in P load reductions and the concomitant return of Lake Erie's resiliency (DePinto et al., 1986; Botts and Muldoon, 2005; Scavia et al., 2014), increases in hypoxia, beach closings and algal biomass since the mid-1990s are indications that Lake Erie has become eutrophic again (Bridgeman and Penamon, 2010; Burns et al, 2005; Michalak et al., 2013; Scavia et al., 2014). The term re-eutrophication has been used to describe this phenomenon (Culver and Conroy, 2012; Scavia et al., 2014).While the causes of eutrophication of Lake Erie in the 1960s and 1970s seemed simple and could be linearly traced to P loadings, the current eutrophication of Lake Erie is highly complex and compounded by interacting stressors such as aquatic invasive species and climate change (Pennuto et al., 2014). The eutrophication of Lake Erie now displays the symptoms of a wicked problem, where all the information is not known and the solution is not clear cut and is highly complex (Xiang, 2013). As such, a new model of governance is needed for the restoration of Lake Erie, a governance model that moves from the old command and control paradigm that worked well in a highly certain world, to one that embraces uncertainty. One such governance model is adaptive governance, as it is the facilitator of adaptive capacity that allows better response in an uncertain environment.This paper introduces the concept of adaptive capacity and shows its relevance to eutrophication of Lake Erie. A framework for assessing adaptive capacity is developed and conceptualized by formulating determinants of adaptive capacity from the literature. These determinants are then validated through semi-structured interviews in a baseline case of Lake Erie, which went from severe nutrient enrichment in the 1970s to significant P reductions in the early 1990s. This paper argues that an analysis of these determinants can show the gaps in building adaptive capacity and can prove valuable in the implementation of actions for nutrient management and hence in the implementation of Annex 4 (Nutrients) under the Great Lakes Water Quality Protocol 2012.Eutrophication of Lake Erie - Baseline CaseThe Laurentian Great Lakes are the largest freshwater body on earth and comprise Lake Superior, Lake Michigan, Lake Huron, Lake Ontario and Lake Erie. All the Great Lakes are subject to a host of anthropogenic stressors, as illustrated in the land use pattern shown in Figure 6.1. Lake Erie is the least forested of all the Great Lakes and has the most intensive farmlands and urban areas. According to Environment Canada and USEPA (1995), 63% of Lake Erie watershed is being farmed while 84% of its shoreline is for residential uses, 35% is used for agriculture and 22% for commercial uses. …

Parameterization of biogeochemical sediment–water fluxes using in situ measurements and a diagenetic model

Abstract. Diagenetic processes are important drivers of water column biogeochemistry in coastal areas. For example, sediment oxygen consumption can be a significant contributor to oxygen depletion in hypoxic systems, and sediment–water nutrient fluxes support primary productivity in the overlying water column. Moreover, nonlinearities develop between bottom water conditions and sediment–water fluxes due to loss of oxygen-dependent processes in the sediment as oxygen becomes depleted in bottom waters. Yet, sediment–water fluxes of chemical species are often parameterized crudely in coupled physical–biogeochemical models, using simple linear parameterizations that are only poorly constrained by observations. Diagenetic models that represent sediment biogeochemistry are available, but rarely are coupled to water column biogeochemical models because they are computationally expensive. Here, we apply a method that efficiently parameterizes sediment–water fluxes of oxygen, nitrate and ammonium by combining in situ measurements, a diagenetic model and a parameter optimization method. As a proof of concept, we apply this method to the Louisiana Shelf where high primary production, stimulated by excessive nutrient loads from the Mississippi–Atchafalaya River system, promotes the development of hypoxic bottom waters in summer. The parameterized sediment–water fluxes represent nonlinear feedbacks between water column and sediment processes at low bottom water oxygen concentrations, which may persist for long periods (weeks to months) in hypoxic systems such as the Louisiana Shelf. This method can be applied to other systems and is particularly relevant for shallow coastal and estuarine waters where the interaction between sediment and water column is strong and hypoxia is prone to occur due to land-based nutrient loads.

Nutrient load apportionment to support the identification of appropriate water framework directive measures

A model for predicting the sources of nutrient loads (phosphorus and nitrogen) to water has been developed to support Water Framework Directive (WFD) implementation. The Source Load Apportionment Model (SLAM) framework described in this paper integrates catchment data and pressure information from point discharges and diffuse sources to enable characterisation of source–pathway–receptor relationships. Hydrogeological controls have a strong impact on nutrient fluxes, particularly in agricultural catchments, and have been incorporated into the diffuse agricultural model (the CCT). Results for the Suir catchment matched the measured loads of nitrogen and phosphorus well, and showed that pasture is the dominant source of nitrogen. The main sources of phosphorus in sub-catchments varied between diffuse agriculture, wastewater and industrial discharges. A relatively small proportion (13%) of the Suir catchment area requires a reduction in phosphorus emissions to achieve Good status. In these areas, model results can be used in conjunction with local knowledge gathered through the WFD characterisation process to identify significant pressures that contribute excessive nutrient loads. An example of assessing load reduction scenarios is presented to illustrate how modelling can support catchment scientists in identifying appropriate measures.

Contrasting effects of nutrient enrichment on below‐ground biomass in coastal wetlands

Summary Anthropogenically enhanced nutrient availability is often cited among the most important drivers of altered ecosystem function and loss of services world‐wide. Although the above‐ground consequences of nutrient enrichment on plant growth patterns are numerous and well documented, below‐ground impacts are less clear but nonetheless critical from a global change perspective. In coastal wetlands, for example, plant–soil–nutrient dynamics directly affect the capacity to sequester carbon as soil organic matter, keep pace with sea level rise and resist storm‐induced erosion. Here, we investigate the effects of excess nutrient loading on below‐ground plant growth in an oligohaline marsh fertilized for 7 years with a factorial combination of nitrogen (N) and phosphorus (P). We used two common assessment procedures, the ingrowth and standing crop methods, to simultaneously quantify distinct aspects of below‐ground plant growth, which are (i) below‐ground biomass accumulation into unexploited open resource space and (ii) in situ, or maintenance, below‐ground biomass of plants in equilibrium with their environment, respectively. Our objective was to determine if plant growth responses to nutrient enrichment differed depending on process and/or biomass component measured. We show that excess N concurrently increased live root biomass accumulation in ingrowth cores and reduced in situ live root standing crop. Similar, albeit non‐significant, response trajectories were apparent for other below‐ground biomass pools using both methods, excepting dead biomass and total standing crop. A review of previously published research supports our results and suggests that nutrient enrichment consistently has contrasting effects on below‐ground plant growth depending on whether biomass accumulation or standing crop is measured, and that living biomass components are most responsive to enhanced nutrient availability. Synthesis. We conclude that eutrophic conditions can be both beneficial and detrimental to ecosystem function by either stimulating below‐ground biomass accumulation in unexploited soil or reducing the below‐ground standing crop required to sustain the nutritional needs of established plants in mature communities. Thus, nutrient enrichment may, in the short‐term, contribute to soil organic matter (i.e. carbon) accumulation by increasing below‐ground growth as plants exploit new resource space. Over the long‐term, however, nutrient enrichment has the potential to negatively impact soil organic matter content as plants equilibrate to excess nutrient availability by down‐regulating below‐ground standing crop.

The threshold responses of phytoplankton community to nutrient gradient in a shallow eutrophic Chinese lake

Excessive nutrient loads resulted in cascading trophic effects and ecosystem responses. Aims of this study were to determine if the thresholds in nutrient gradient related to phytoplankton community composition could be identified in eutrophic lake, and further to analyze the change of phytoplankton assemblage along the nutrient concentration based on Threshold Indicator Taxa ANalysis (TITAN). The results presented the significant community thresholds estimate for negative taxa declining at 1.650mg/L TN and 131.5μg/L TP, as well as simultaneously increasing for positive taxa at 1.665mg/L TN and 151.5μg/L TP along nutrient enrichment gradient. However, there was unremarkable change point determined for TN:TP ratios in Lake Dianchi. Elevated TN and TP altered the phytoplankton assemblage, even may induce the fade of algal blooms across the threshold in the hypertrophic lake. The findings could provide implications for deeply deciphering abrupt transitions for phytoplankton assemblage and developing nutrient tactics to protect the lake ecosystems.

Spatiotemporal Dynamics of Microcystin Variants and Relationships with Environmental Parameters in Lake Taihu, China.

Excessive anthropogenically-caused nutrient loading from both external and internal sources has promoted the growth of cyanobacteria in Lake Taihu from 2005 to 2014, suggesting increased production and release of cyanotoxins. In order to explain the spatial distribution and temporal variation of microcystins (MCs), the intracellular concentrations of MCs (MC-LR, -RR and -YR, L, R and Y are abbreviations of leucine, arginine and tyrosine) were monitored monthly from July 2013 to June 2014. Three MC variants are present simultaneously in Lake Taihu; the MC-LR and -RR variants were dominant (accounting for 40% and 39% of the total), followed by MC-YR (21%). However, MC-YR accounted for a higher proportion in colder months, especially in March. The highest concentrations of intracellular MCs were found in July and October when cyanobacteria cell density also reached the maximum. The average concentrations of MC-LR, -RR and -YR in July were 4.69, 4.23 and 2.01 μg/L, respectively. In terms of the entire lake, toxin concentrations in northern parts were significantly higher than the eastern part in summer, when MC concentrations were several times higher than the guideline value by WHO throughout much of Lake Taihu. Results from correlation and redundancy analysis (RDA) showed that total MCs, including all variants, were strongly and positively correlated with cyanobacteria cell density, water temperature, total phosphorus (TP) and pH, whereas each variant had different correlation coefficients with each of the considered environmental variables. MC-RR showed a stronger relationship with temperature, in contrast to MC-YR and -LR. Dissolved inorganic carbon (DIC) showed a negative relationship with each variant, suggesting that rising DIC concentrations may inhibit cyanobacterial growth and thereby reduce MC production in the future.

Cyanobacterial bloom dynamics in Lake Taihu

Lake Taihu is the third largest freshwater lake in China and serves as an important drinking water source for the local populace;however,decades of excessive nutrient loading fueled by anthropogenic activities have resulted in hypertrophic conditions,promoting the annual formation of nuisance phytoplankton blooms(Chen et al.,2003;Duan et al.,2009)

Nitrogenous nutrients promote the growth and toxicity of Dinophysis acuminata during estuarine bloom events.

Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome most commonly caused by dinoflagellates within the genus Dinophysis. While blooms of harmful algae have frequently been linked to excessive nutrient loading, Dinophysis is a mixotrophic alga whose growth is typically associated with prey availability. Consequently, field studies of Dinophysis and nutrients have been rare. Here, the temporal dynamics of Dinophysis acuminata blooms, DSP toxins, and nutrients (nitrate, ammonium, phosphate, silicate, organic compounds) were examined over four years within two New York estuaries (Meetinghouse Creek and Northport Bay). Further, changes in the abundance and toxicity of D. acuminata were assessed during a series of nutrient amendment experiments performed over a three year period. During the study, Dinophysis acuminata blooms exceeding one million cells L-1 were observed in both estuaries. Highly significant (p<0.001) forward stepwise multivariate regression models of ecosystem observations demonstrated that D. acuminata abundances were positively dependent on multiple environmental parameters including ammonium (p = 0.007) while cellular toxin content was positively dependent on ammonium (p = 0.002) but negatively dependent on nitrate (p<0.001). Nitrogen- (N) and phosphorus- (P) containing inorganic and organic nutrients significantly enhanced D. acuminata densities in nearly all (13 of 14) experiments performed. Ammonium significantly increased cell densities in 10 of 11 experiments, while glutamine significantly enhanced cellular DSP content in 4 of 5 experiments examining this compound. Nutrients may have directly or indirectly enhanced D. acuminata abundances as densities of this mixotroph during experiments were significantly correlated with multiple members of the planktonic community (phytoflagellates and Mesodinium). Collectively, this study demonstrates that nutrient loading and more specifically N-loading promotes the growth and toxicity of D. acuminata populations in coastal zones.

A model of the three-dimensional hydrodynamics, transport and flushing in the Bay of Quinte

Abstract The Bay of Quinte, Ontario, receives excessive nutrient loads and suffers from poor water quality. The 70 km long z-shaped bay traps the nutrients due to limited flushing with Lake Ontario, leading to increased nutrient residence times. Therefore, it is important to understand the three-dimensional hydrodynamic conditions within the bay, as these drive horizontal transport, dilution of nutrient rich inflows and water exchange to the lake. In this study, the effects of meteorological forcing, river inflows and Lake Ontario exchange on the hydrodynamics and mixing were investigated using a numerical model. The model was validated against temperature time series and profile data, with a maximum root-mean-square deviation

A classification system for large reservoirs of the contiguous United States.

Degradation of reservoir fish habitat has become a serious concern. Habitat issues-such as sedimentation, excessive nutrient loadings, and lack of submerged structure-may emerge and worsen over time and are accompanied by undesirable shifts in the fish community and fisheries. To prioritize habitat rehabilitation efforts in reservoirs, we developed a classification system for large reservoirs in the contiguous U.S. We used a four-step classification approach based on over 50 variables descriptive of habitat impairment in a sample of almost 1300 reservoirs. To account for the broad geographic heterogeneity in climate and landscape, reservoirs were assigned to a spatial framework relevant to aquatic resources, selected based on how well it recognized regional differences in fish habitat. To account for differences among reservoirs within geographical regions, we used cluster analysis to identify classes of reservoirs with similar characteristics. Classes were compared regarding habitat impairment, the fish community, the recreational fishery, and other variables from an external dataset to seek support for the classification system. A method for classifying new reservoirs not included in the original sample was also developed. The resulting classification system identified nine geographical regions distributed throughout the contiguous U.S. and 24 reservoir classes within the nine regions. The system can serve as the framework for a reservoir assessment mechanism. Our approach may be applicable elsewhere a broad-scale dataset is not available and needs to be obtained quickly and inexpensively, whether in regards to fish habitat or other environmental information needs.

Remediation effect of pond–ditch circulation on rural wastewater in southern China

To mitigate water pollution caused by rapid urbanization in the rural areas of China, it is urgent to develop suitable wastewater treatment technologies, which are socio-economic, environmentally sustainable and easily maintained. This study investigates the remediation effect of a pond–ditch circulation system on water quality. This system is composed of connected ponds and ditches in rural areas. We constructed the treatment systems as follows: system I (S1) was circulated 24h/day (13.2L/h), system II (S2) was static with macrophytes, and system III (S3) was circulated with macrophytes. Our results indicated that after 60 days of treatment, the levels of the total nitrogen, total phosphorus, ammonia nitrogen, chemical oxygen demand, chlorophyll a and turbidity of water significantly decreased in the ponds/ditches of S1 and S3. Similar significant decreases of these parameters were observed in the water of the ditch in S2, whereas the concentrations of TN, TP and NH4+-N of water from the two ponds in S2 increased. Moreover, the increase of the species numbers and the diversity index of zooplankton and the decrease of heterotrophic index in three ponds/ditches of S1 and S3 and the ditch of S2 demonstrated the improvement in water quality. The significant relationship between the zooplankton community structure and the environmental variables was confirmed by redundancy analysis (RDA) and Pearson’s correlation analysis. In conclusion, the pond–ditch circulation system can effectively remove excessive nutrient loads and improve water quality and hence represents a simple and economical solution for the restoration of a degraded rural water environment.

Historical accumulation of N and P and sources of organic matter and N in sediment in an agricultural reservoir in Northern China.

Agriculture has significantly intensified in Northern China since the 1980s. This intensification has caused a series of simultaneous lake ecological environment problems in this area. However, little is known about the role of agricultural intensification in historical nutrient dynamics and lake eutrophication processes. The Yanghe reservoir, a typical artificial reservoir characterized by high-yield grain production in Northern China, has been suffering from serious eutrophication and water quality deterioration. This study evaluates the effect of agricultural intensification on nutrient retention and source in the sediments using (210)Pb and (137)Cs dating techniques combined with stable C and N isotopes (δ(13)C, δ(15)N) and total organic carbon/total nitrogen, as well as total nitrogen (TN), total phosphorus (TP), and P fractions. Results suggested that agricultural intensification was keys to the accumulation of nutrients and was a source of organic matter (OM) and N in sediment for the past three decades. N and P pollution started in the 1980s and worsened from the 1990s. Good water quality status and steady sedimentary environment with low nutrient content (mean concentrations of TN and TP were 815 and 387 mg kg(-1), respectively) were observed before the 1980s. Sediment OM was primarily derived from aquatic plants, whereas N was primarily derived from soil erosion and aquatic plants. However, water quality began to deteriorate while sediment nutrient content began to increase after the 1980s, with values of 1186 mg kg(-1) for TN and 434 mg kg(-1) for TP in 1989. Sediment OM was primarily derived from C3 (sweet potato) and aquatic plants, and the major sources of N were soil erosion, fertilizer, and sewage, which accompany the rapid development of agriculture in the watershed. Following the further growth of grain production and fertilizers, excessive external nutrient loading has resulted in dramatic water quality and ecosystem deterioration since 1990. The increasing rate of TN and TP contents was also augmented during these periods, reaching as high as 2624 and 846 mg kg(-1) in surface sediment, respectively. In addition, sources of OM and N in sediment were similar to those in the 1980s, but the contribution of aquatic organic N in sediment has continued to increase (aquatic organic N that accounts for TN increased from 14.5% before the 1980s to 48% in 2007). This condition could be attributed to the impact of frequent "water bloom" and recession of aquatic plant due to worsening water pollution.