Phosphorus Load Reduction Research Articles

Modeling the response of phytoplankton to reduced external nutrient load in a subtropical Chinese reservoir using DYRESM-CAEDYM

Cui Y, Zhu G, Li H, Luo L, Cheng X, Jin Y, and Trolle D. Modeling the response of phytoplankton to reduced external nutrient load in a subtropical Chinese reservoir using DYRESM-CAEDYM. Lake Reserv Manage. 32: 146--157.The DYRESM-CAEDYM model was used to quantify the potential effects of reductions in external nutrient loads to the Shahe Reservoir in China, with an emphasis on effects on phytoplankton biomass. DYRESM-CAEDYM was calibrated using field data for a 2-year period and validated against a separate 1-year period. Simulated values for water temperature, dissolved oxygen, total nitrogen, total phosphorus, and chlorophyll a showed good agreement with field measurements. The model tended to underestimate peak values of inorganic nutrients such as ammonium, nitrate, and phosphate, with phosphate levels close to detection limits in both observed and simulated values. The model successfully captured seasonal phytoplankton succession, indicating spring peaks of diatom biomass and summer peaks of cyanophytes. Scenarios in which different reductions in external loading were applied suggest that simultaneous reductions in both external nitrogen and external phosphorus loading is more effective in controlling phytoplankton biomass than reducing input of either nutrient alone. Diatoms responded more strongly to load reductions in phosphorus input than nitrogen load, whereas cyanophytes showed the opposite pattern. A combined 25% reduction in the external loading of both nutrients could significantly decrease phytoplankton biomass in the reservoir below the 7 μg/L chlorophyll a required by drinking water standards, and the study indicated that DYRESM-CAEDYM can be a useful management tool for eutrophication control.

Farming system transformation yields significant reduction in nutrient loading: Case study of Hongze Lake, Yangtze River Basin, China

China dominates aquaculture production accounting for 65.7% of the global total of 76.3milliontonnes. In view of increasing environment concerns resulting from intensification of aquaculture practices there is a notable shift of aquatic farming practices in China. In this study, the gross reduction of nitrogen (N) and phosphorus (P) loading into Hongze Lake, 1597km2 (118.48–118.72° E and 33.36–33.38° N), of average water depth of 1.77m, the fourth largest freshwater lake in China, resulting from the transformation of intensive polyculture of Chinese major carps to farming mitten crab (Eriocheir sinensis (Milne-Edwards, 1854)) is presented. This transformation occurred since the 1990s. Current mitten crab production is 59,932tonnes, in 40,802ha located in 17 farming areas in the reclaimed wetlands around Hongze Lake. Mass balance models were used to calculate the nutrient loading. The net N and P in effluent from different mitten crab farming areas ranged from 8.2 to 22.6kgha−1cycle−1 (mean 14.2kgha−1cycle−1), and from 1.3 to 3.5kgha−1cycle−1 (mean 2.2kgha−1cycle−1), respectively. The total net N and P in effluent from mitten crab farming sector were 579tcycle−1 and 90tcycle−1, respectively. Compared with fish polyculture prior to 1990s, the net N and P in effluent from mitten crab farming decreased by 2334tcycle−1 and 494tcycle−1, respectively. The above results are discussed in the light of mitten crab farming practices of using macrophytes that improve water quality and also provide refuge and natural food favored by mitten crab. Statement of relevanceThe present study attempts to estimate nitrogen and phosphorus loading and discharge from the mitten crab farming sector around Hongze Lake using the nutrient balance. The changes in nitrogen and phosphorus loading resulting from the transformation of intensive carp polyculture prior to 1990s to mitten crab farming in recent decades in the reclaimed wetlands around Hongze Lake were also evaluated. It is expected that the present study will provide additional information to improve environmental sustainability of aquatic farming system in China.

Effects of Livestock Exclusion and Stream Restoration on the Water Quality of a North Carolina Stream

The objective of this project was to document the effect of livestock exclusion and stream restoration on the water quality of two streams. Water quality monitoring was conducted prior to and after the installation of livestock exclusion fencing and varying degrees of stream restoration on the two streams. The monitored reaches of both streams were located in a dairy cow pasture with the same management in that, prior to fencing and stream restoration (pre-BMP) implementation, cows had unlimited access to the stream channel and after (post-BMP) the cows were fenced out. Rainfall and discharge were monitored continuously, and flow-proportional samples were collected upstream and downstream of the two monitored reaches during storm events. Non-storm grab samples were also collected at each monitoring station. Samples were analyzed for nitrogen, phosphorus, and sediment concentrations. Water quality monitoring occurred for approximately three years prior to (pre-BMP) and 1.7 years following (post-BMP) fencing and stream restoration. Livestock exclusion fencing and limited stream restoration on a 488 m long reach of one stream resulted in statistically significant reductions in total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH 3 -N), total phosphorus (TP), and total suspended residue (TSR) storm event loads of 41%, 59%, 54%, and 67%, respectively, compared to the pre-BMP loads. However, the proportion of the reduction attributable to exclusion fencing, stream restoration, or fewer cows in the pasture could not be determined. The second stream had a full restoration in that the streambed was raised, moved, and completely reconstructed over the entire 134 m long monitored reach. Post-BMP monitoring documented significant differences in NH 3 -N (decreased), and NOx-N (increased) loads and no change in TKN, TP, TSR, and total nitrogen (TN) loads from the upstream to the downstream monitoring station. These results indicated that there was no significant treatment effect of the restored stream channel on instream pollutant loads.

Geo-engineering experiments in two urban ponds to control eutrophication

Many urban ponds experience detrimental algal blooms as the result of eutrophication. During a two year field experiment, the efficacy of five in situ treatments to mitigate eutrophication effects in urban ponds was studied. The treatments targeted the sediment phosphorus release and were intended to switch the ponds from a turbid phytoplankton-dominated state to a clear-water state with a low phytoplankton biomass. Two eutrophic urban ponds were each divided into six compartments (300–400 m2; 210–700 m3). In each pond the following treatments were tested: dredging in combination with biomanipulation (involving fish biomass control and the introduction of macrophytes) with and without the addition of the flocculant polyaluminiumchloride, interception and reduction of sediment phosphorus release with lanthanum-modified bentonite (Phoslock®) in combination with biomanipulation with and without polyaluminiumchloride; biomanipulation alone; and a control. Trial results support the hypothesis that the combination of biomanipulation and measures targeting the sediment phosphorus release can be effective in reducing the phytoplankton biomass and establishing and maintaining a clear-water state, provided the external phosphorus loading is limited. During the experimental period dredging combined with biomanipulation showed mean chlorophyll-a concentrations of 5.3 and 6.2 μg L−1, compared to 268.9 and 52.4 μg L−1 in the control compartments. Lanthanum-modified bentonite can be an effective alternative to dredging and in combination with biomanipulation it showed mean chlorophyll-a concentrations of 5.9 and 7.6 μg L−1. Biomanipulation alone did not establish a clear-water state or only during a limited period. As the two experimental sites differed in their reaction to the treatments, it is important to choose the most promising treatment depending on site specific characteristics. In recovering the water quality status of urban ponds, continuing attention is required to the concurrent reduction of external phosphorus loading and to maintaining an appropriate fish community.

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.

Long-term temporal and spatial trends in eutrophication status of the Baltic Sea.

Much of the Baltic Sea is currently classified as 'affected by eutrophication'. The causes for this are twofold. First, current levels of nutrient inputs (nitrogen and phosphorus) from human activities exceed the natural processing capacity with an accumulation of nutrients in the Baltic Sea over the last 50-100 years. Secondly, the Baltic Sea is naturally susceptible to nutrient enrichment due to a combination of long retention times and stratification restricting ventilation of deep waters. Here, based on a unique data set collated from research activities and long-term monitoring programs, we report on the temporal and spatial trends of eutrophication status for the open Baltic Sea over a 112-year period using the HELCOM Eutrophication Assessment Tool (HEAT 3.0). Further, we analyse variation in the confidence of the eutrophication status assessment based on a systematic quantitative approach using coefficients of variation in the observations. The classifications in our assessment indicate that the first signs of eutrophication emerged in the mid-1950s and the central parts of the Baltic Sea changed from being unaffected by eutrophication to being affected. We document improvements in eutrophication status that are direct consequences of long-term efforts to reduce the inputs of nutrients. The reductions in both nitrogen and phosphorus loads have led to large-scale alleviation of eutrophication and to a healthier Baltic Sea. Reduced confidence in our assessment is seen more recently due to reductions in the scope of monitoring programs. Our study sets a baseline for implementation of the ecosystem-based management strategies and policies currently in place including the EU Marine Strategy Framework Directives and the HELCOM Baltic Sea Action Plan.

Confronting tipping points: Can multi-objective evolutionary algorithms discover pollution control tradeoffs given environmental thresholds?

This study contributes a stochastic, multi-objective adaptation of the classic environmental economics Lake Problem as a computationally simple but mathematically challenging benchmarking problem. The Lake Problem considers a hypothetical town by a lake, which hopes to maximize its economic benefit without crossing a nonlinear, and potentially irreversible, pollution threshold. Optimization objectives are maximize economic benefit, minimize phosphorus in the lake, maximize the probability of avoiding the pollution threshold, and minimize the probability of drastic phosphorus loading reductions in a given year. Uncertainty is introduced through a stochastic natural phosphorus inflow. We performed comprehensive diagnostics using six algorithms: the Borg multi-objective evolutionary algorithm (MOEA), MOEA/D, epsilon-MOEA, the Non-dominated Sorting Genetic Algorithm II (NSGAII), epsilon-NSGAII, and Generalized Differential Evolution 3 (GDE3) to evaluate their controllability, reliability, efficiency, and effectiveness. Our results show only the self-adaptive search of the Borg MOEA was capable of performing well on this nontrivial benchmarking problem.

Métodos de control de las floraciones de cianobacterias en aguas continentales

Blooms of phytoplankton organisms, especially cyanobacteria represent an important economic and ecological problem in the management of water and aquatic ecosystems. The biomass increment, besides causing aesthetic problems, such as the appearance of foams and odors, alters the taste of drinking water and causes deoxygenation and water chemistry changes when it decomposes compromising the survival of aquatic organisms. However, blooms of cyanobacteria are the most studied and known as these organisms produce bioactive metabolites (cyanotoxins) that constitute a serious environmental problem with serious implications on human and animal health. Therefore, the need to resolve the problems associated with cyanobacteria has led to the use of multiple techniques to alleviate their uncontrolled development and improve water quality. This paper is a review of methods for cyanobacterial blooms control in inland waters. All these techniques are related to the factors that regulate the primary production. Thus, the reduction of the external phosphorus loading is sought through the control of inputs in the watershed (agriculture, sanitation, industry, etc.), but also by acting directly on the water body. Moreover, within this intervention strategy on the primary factors controlling the growth of autotrophs, techniques to limit the incident light have also been developed. Mechanical control has been addressed by physical removal of the biomass of cyanobacteria, application of ultrasounds, etc. For the chemical controls a variety of compounds with very different effects, ranging from the application of algaecides or herbicides to oxidants and other substances such as Cu, MnO4K2, H2O2, etc. have been used. Simultaneously, a large number of agents for biological control have been tested with varying success (e.g. viruses, bacteria, protozoa, fungi, aquatic plants, fish) and plant materials in aerobic decomposition have been widely used.

Response of diatom and dinoflagellate lifeforms to reduced phosphorus loading: A case study in the Thau lagoon, France

The basin of Thau in southern France is a shallow, weakly flushed lagoon which is an important location for oyster cultivation. Phytoplankton analyses were carried out in 1975–1976 and then (almost) continuously since 1987. We report an investigation of ‘the balance of organisms’ in phytoplankton in relation to reductions in phosphorus loading, using two new tools based on phytoplankton lifeforms: the Plankton Index for Phytoplankton (PIp); Euclidean distance in state-space. Our results show the utility of the tools for analysing changes in the ‘balance of organisms’ at the level of functional groups (in our study diatoms and dinoflagellates), but also illustrate the difficulties in demonstrating the reversal of human impacts resulting from eutrophication.The comparison between 1987–89 and 1976 showed the expected ‘de-eutrophication’ due to the reduction in dissolved inorganic phosphate (DIP), with a decrease in dinoflagellate abundance. Since 1989, year-to-year variation in annual mean concentrations of DIP may have contributed to inter-annual variability in the balance of the two lifeforms, but the data suggest that the system has remained in a dynamically stable regime because: (1) there was no long-term trend in Euclidean distance from the reference; and (2) there was no increase in inter-annual variability about the time-series mean Euclidean distance suggesting there has been no decrease in resilience which might signal a regime change.Integrated management of human activities will be required to manage (and reduce) total P in the system. Monitoring phytoplankton and nutrients concentrations to determine how primary production and the balance of species respond to further changes in the nutrient status of the lagoon should be an integral part of any management programme.

TMDL reevaluation: reconciling internal phosphorus load reductions in a eutrophic lake

Total maximum daily loads (TMDLs) are assigned to impaired waterbodies and provide a prescription for recovery. It is implicit that both the existing conditions and targets identified in a TMDL are based on credible and accurate information, ensuring that management actions directed to recovery are appropriate and effective. We evaluated the TMDL for phosphorus in Bear Lake, Michigan, to assess if the prescribed reduction was appropriately based on existing annual internal loads. We developed 5 different annual internal load scenarios based on phosphorus release rates from laboratory-based sediment incubations and diel dissolved oxygen measurements, ranging from very conservative to very liberal estimates of phosphorus release. The most realistic scenarios indicate that the previously established TMDL for internal phosphorus loading is 3–7 times greater than what actually occurs in Bear Lake. Based on our assessment, Bear Lake is likely already meeting the TMDL internal loading target, without the implementation of any management action. Thus, management efforts aimed at reducing the water column phosphorus concentration to reach the TMDL target should instead be directed at controlling the external phosphorus load.

Relative importance of phosphorus, invasive mussels and climate for patterns in chlorophyll a and primary production in Lakes Michigan and Huron

Summary Lakes Michigan and Huron, which are undergoing oligotrophication after reduction of phosphorus loading, invasion by dreissenid mussels and variation in climate, provide an opportunity to conduct large‐scale evaluation of the relative importance of these changes for lake productivity. We used remote sensing, field data and an information‐theoretic approach to identify factors that showed statistical relationships with observed changes in chlorophyll a (chla) and primary production (PP). Spring phosphorus (TP), annual mean chla and PP have all declined significantly in both lakes since the late 1990s. Additionally, monthly mean values of chla have decreased in many but not all months, indicating altered seasonal patterns. The most striking change has been the decrease in chla concentration during the spring bloom. Mean chlorophyll a concentration was 17% higher in Lake Michigan than in Lake Huron, and total production for 2008 in Lake Michigan (9.5 tg year−1) was 10% greater than in Lake Huron (7.8 tg year−1), even though Lake Michigan is slightly smaller (by 3%) than Lake Huron. Differences between the lakes in the early 1970s evidently persisted to 2008. Invasive mussels influenced temporal trends in spring chla and annual primary production. However, TP had a greater effect on chla and primary production than did the mussels, and TP varied independently from them. Two climatic variables (precipitation and air temperature in the basins) influenced annual chla and annual PP, while the extent of ice cover influenced TP but not chla or primary production. Our results demonstrate that observed temporal patterns in chla and PP are the result of complex interactions of P, climate and invasive mussels.

Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses.

Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for movement of sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine the reduction in drainage effluent total suspended sediment (TSS) and phosphorus (P) concentrations and loads when open surface inlets were replaced with blind (in gravel capped with 30 cm of soil) or gravel (in very coarse sand/fine gravel) inlets. In Indiana, a pair of closed depressions in adjacent fields was fitted with open inlet tile risers and blind inlets in 2005 and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season for years 2006 to 2013 showed that TSS loads were 40.4 and 14.4 kg ha event for tile risers and blind inlets, respectively. Total P (TP) and soluble reactive P (SRP) loads were 66 and 50% less for the blind inlets, respectively. In Minnesota, TSS and SRP concentrations were monitored for 3 yr before and after modification of 24 open inlets to gravel inlets in an unreplicated large-field on-farm study. Median TSS concentrations were 97 and 8.3 mg L and median SRP concentrations were 0.099 and 0.064 mg L for the open inlet and gravel inlet periods, respectively. Median TSS and SRP concentrations were elevated for snowmelt vs. non-snowmelt seasons for open and gravel inlets. Both replacement designs reduced suspended sediment and P concentrations and loads. The Indiana study suggests blind inlets will be effective beyond a 10-yr service life.

Subsoil Phosphorus Loss: A complex problem with no easy solutions

Subsoil Phosphorus Loss: A complex problem with no easy solutions

Using SWAT to determine reference nutrient conditions for small and large streams

Developing reference criteria for nutrient conditions on streams can be difficult especially in heavily farmed or urbanized regions where most of the landscape has been impacted by human development. SWAT (soil water assessment tool) simulations permit the removal of the anthropogenic impacted land use, allowing the simulation of natural conditions and a prediction of reference conditions. A Genesee River watershed simulation was developed to determine the nutrient and sediment contributions of subbasins of the Genesee River under the current human-impacted conditions and contrasted against natural conditions. Nutrient boundary values estimated for Genesee basin small wadeable streams (34.3μgP/L) were nearly identical to those calculated by others for small, wadeable streams (30.7μgP/L). For large streams, the simulation-based boundary total phosphorus (TP) value (75.8μgP/L) of the Genesee River was high compared to other observations in New York State (30μgP/L). Causes in the variability in large stream reference values include inappropriate use of regional reference conditions, stream bank erosion, basin geology, soil type, and catchment area. When river bank stabilization was added to the simulation, a 34.3% reduction in phosphorus loading was observed, resulting in a boundary value of ~54μgP/L. This reduction in the simulated sediment load suggested that the Genesee River has a higher natural sediment and TP load than most streams in NYS. SWAT is an effective tool for simulations of small streams and may be an effective method in determining reference conditions for large rivers.

Trophic state responses of Onondaga Lake, New York, to reductions in phosphorus loading from advanced wastewater treatment

This study evaluated the response of previously culturally hypereutrophic Onondaga Lake, New York, to major reductions in phosphorus (P) loading from a municipal wastewater treatment plant achieved over a 35-year period. Analysis of the response was based on long-term monitoring of effluent total P concentration (TPMetro) and a robust array of in-lake metrics of trophic state, including (1) TP, (2) chlorophyll a (Chl-a), (3) Secchi disk depth, (4) areal hypolimnetic oxygen deficit (AHOD), (5) the downward flux of volatile suspended solids, and (6) the minimum dissolved oxygen concentration in the upper waters during fall turnover. Substantial positive responses, which were significantly linearly related to the decreases in TPMetro, were documented for all of the metrics over the monitoring period. For example, a 91% reduction in TPMetro resulted in reductions of 84% and 59% in Chl-a and AHOD, respectively. The changes depict a transformation from hypereutrophy to upper mesotrophy, with the exception of AHOD values that remain in the eutrophic range. The delayed response of AHOD reflects slower sediment diagenesis processes. The relationships among the metrics of trophic state are considered in the context of literature expressions, accepted paradigms, and limitations related to variations in food web effects. Empirical models that include the effects of multiple drivers on interannual variations in contemporary trophic state metrics were developed and applied to forecast variability under existing conditions. This case study contributes to the scientific literature describing lake rehabilitation through reductions in P loading.

Nutrient Fluxes and Their Impact on the Phytoplankton in a Shallow Coastal Lake

Data on nutrient concentrations and phytoplankton growth was analyzed in Lake Gardno, representing a separate group of coastal lakes within the Polish abiotic typology according to the Water Framework Directive. The aim of this work was to identify sources of nutrient variability in lake water and consequences of this variability for phytoplankton growth. Phytoplankton composition was dominated by green algae, present in high biovolumes throughout the year, and cyanobacteria, whose elevated biovolumes were noted at temperatures above 13oC. Production of phytoplankton was often light-limited throughout the vegetation period (changing on a day-to-day basis). Low N-to-P ratio, the presence of nitrogen-fixing cyanobacteria, and Carlson’s trophic state indices (TSI) analysis indicated also possible nitrogen limitations of primary production during the vegetation period. No phosphorus limitation was indicated. Possible nitrogen limitation was a result of in-lake modification of the N-to-P ratio compared to external N-to-P ratio in nutrient loads discharged by the freshwater inflow. Lake Gardno was a substantial sink of nitrogen discharged by the Łupawa River, probably due to denitrification. Nutrient budget for the 2006-08 period revealed 50% loss of nitrogen in a lake, whereas the phosphorus budget did not reveal substantial phosphorus retention. From a management perspective, the study indicates the importance of reduction of phosphorus loads discharged to the lake, which could prevent further development of cyanobacterial blooms stimulated by low N-to-P ratio.

Correlation of serum parathyroid hormone with mineral bone disease in chronic kidney disease patients

Background: Mineral bone disease (MBD) is a systemic disorder of mineral and bone metabolism due to chronic kidney disease (CKD). Bone disease in CKD is due to secondary hyperparathyroidism. Serum intact parathyroid hormone (iPTH) level estimation is a potential noninvasive method for the diagnosis of MBD at early stage. Aim: Treating renal bone disease should be one of the primary aims of therapy for CKD. Evaluation of the biochemical parameters of CKD-MBD (primarily phosphorus, calcium, parathyroid hormone, and Vitamin D levels) as early as CKD stage 3, and an assessment of bone status (by the best means available), should be used to guide treatment decisions. The adverse effects of high phosphorus intake relative to renal clearance (including stimulation of hyperparathyroidism) precede hyperphosphatemia, which presents late in CKD. Early reduction of phosphorus load may ameliorate these adverse effects. Evidence that calcium load may influence progression of vascular calcification with effects on mortality, should also be considered when choosing the type and dose of phosphate binder to be used. MBD in CKD has high morbidity and mortality and hence it is important to detect it at an early stage. iPTH levels can be highly sensitive and it is one of the useful noninvasive biochemical parameters to detect MBD in CKD. Materials and Methods: This was an observational study carried out in a tertiary care teaching hospital. The study involved 60 patients of CKD. Detailed history, physical examination, and biochemical parameters were assessed in all of them. Results: There was a significant association between hypertension, diabetes with nephropathy, and highly significant association between serum iPTH and raised blood urea levels in MBD group, however there was no significant association between duration of CKD, hemoglobin, creatinine, uric acid, phosphorous, calcium, and alkaline phosphatase with MBD. Conclusions: MBD in CKD can be detected at early stage by the use of noninvasive methods of estimation of serum iPTH levels.

Effects of nitrogen and phosphorus load reduction on benthic phosphorus release in a riverine lake

The Lower Havel in Berlin is a polymictic riverine lake, thermally stratified for some days or weeks in summer. It is characterized by a relatively high mean total phosphorus concentration (145 µg l−1) and frequent cyanobacteria mass development in summer. We quantified the potentially mobile P pool in sediments, determined P fluxes based on conventional dialysis sampler-, gel probe- and benthic chamber measurements, and combined this with column experiments and P budget calculations to evaluate whether a) a reduction of P loading would be counterbalanced by P release from sediment, and b) release of redox sensitive P would even increase with reduction of nitrogen loading. The potentially mobile P pool was relatively small (228 t) compared to mean annual external load (190 t a−1) and gross P release (1.2–36 mg m−2 day−1), and was thus of little relevance for long-term P availability. Despite 38 % of P in the sediment being redox sensitive, the seasonal course of P gross release was mainly driven by redox independent organic matter mineralization of diagenetically young surface sediment. Under anoxic conditions, P release was higher than under oxic conditions and to some extent controlled by nitrate under laboratory conditions. However, ambient nitrate availability was too low to affect P release which was more dependent on mineralization and Fe availability than on redox. Therefore, the Lower Havel would benefit from P load reduction but internal P loading would be largely unaffected from further N load reduction.

Estimating effects of reforestation on nitrogen and phosphorus load reductions in the Lower Yazoo River Watershed, Mississippi

Surface water quality in the Lower Mississippi River Basin (LMRB) and the adjacent Gulf of Mexico has degraded over the past several decades primarily due to deforestation to agricultural lands and the loss of wetlands. This study investigated the benefits of reforestation upon nitrate–nitrogen (NO3−N) and orthophosphate (PO43−) load reductions in the Lower Yazoo River Watershed (LYRW) within the LMRB using the BASINS-HSPF model. The model was calibrated and validated with available experimental data prior to its applications. Two simulation scenarios were then performed: one was chosen to predict the NO3−N and PO43− loads without reforestation and the other was selected to estimate the impacts of reforestation upon NO3−N and PO43− load reductions following the conversion of 25, 50, 75, and 100% of the agricultural lands (with most lands near or in the batture of the streams) into forests. In general, an increase in forests reduced NO3−N and PO43− loads and occurred because forest soils enriched in organic matter absorb water and nutrients and reduce the surface water runoff. Overall, a two-fold increase in forest land would result in approximately two-fold decrease in annual average NO3−N and PO43− loads. On average, over a 10-year simulation, the specific NO3−N and PO43− load reductions were, respectively, 0.06 and 0.004ton/ha/y. Although the annual average NO3−N and PO43− loads always decreased with increasing forest land conversion, the optimal specific NO3−N and PO43− load reductions were found at a 75% reduction of agricultural land for the simulation conditions used in this study. Additionally, the annual average NO3−N load was about 16 times higher than that of PO43− in the LYRW. This study suggests that reforestation in or around the batture of streams is a beneficial practice for NO3−N and PO43− load reductions.

Cattle Fencing BMP Can Reduce Phosphorus Loads from Florida Ranches

BMPs are an important tool in helping the state and individual landowners protect and enhance state’s waters. Given the water quality issues facing Lake Okeechobee and other sensitive water bodies, the importance of BMP implementation has increased since their official establishment as part of the FWRA. In order to ensure that BMPs are reducing nutrient loadings, on-farm research is needed to verify BMP effectiveness. A four-year study was conducted to evaluate the effectiveness of the cow/calf stream fencing BMP. The study concluded that the BMP did reduce the amount of P being discharged from the ranch. This BMP should continue to be included in the cow/calf BMP manual, and, hopefully, its widespread implementation will help the state in meeting its TMDLs. This 3-page fact sheet was written by Sanjay Shukla, Wendy D. Graham, Alan Hodges, and James M. Knowles, and published by the UF Department of Agricultural and Biological Engineering, May 2014.
 AE501/AE501: Cattle Fencing BMP Can Reduce Phosphorus Loads from Florida Ranches (ufl.edu)