Global mapping of freshwater nutrient enrichment and periphyton growth potential.

Periphyton (viz. algal) growth in many freshwater systems is associated with severe eutrophication that can impair productive and recreational use of water by billions of people. However, there has been limited analysis of periphyton growth at a global level. To predict where nutrient over-enrichment and undesirable periphyton growth occurs, we combined several databases to model and map global dissolved and total nitrogen (N) and phosphorus (P) concentrations, climatic and catchment characteristics for up to 1406 larger rivers that were analysed between 1990 and 2016. We predict that 31% of the global landmass contained catchments may exhibit undesirable levels of periphyton growth. Almost three-quarters (76%) of undesirable periphyton growth was caused by P-enrichment and mapped to catchments dominated by agricultural land in North and South America and Europe containing 1.7B people. In contrast, undesirable periphyton growth due to N-enrichment was mapped to parts of North Africa and parts of the Middle East and India affecting 280 M people. The findings of this global modelling approach can be used by landowners and policy makers to better target investment and actions at finer spatial scales to remediate poor water quality owing to periphyton growth.

Runoff water quality from broiler litter-amended tall fescue in response to natural precipitation in the Ozark Highlands.

The Arkansas poultry industry produced more than 1.2 billion broiler chickens (Gallus gallus domesticus) and generated approximately 1.3 million Mg of broiler litter in 2002. High transportation costs of relocating broiler litter have led to annual land applications near poultry houses, increasing concern for potential surface water contamination from runoff. The objective of this study was to evaluate the effect of broiler litter application rate on runoff water quality in response to natural precipitation. Six plots (1.5 by 6.0 m), located on a Captina silt loam (finesilty, siliceous, active, mesic Typic Fragiudult), were amended with fresh broiler litter at 0, 5.6, and 11.2 Mg ha(-1) (control, low, and high litter treatments, respectively) once annually for 4 yr (May 2003 through April 2007). Runoff collected after each runoff-producing event was analyzed for soluble nutrients and metals. Cumulative runoff did not differ among litter treatments over the 4-yr study. At times, flow-weighted mean (FWM) concentrations of As from all litter treatments exceeded the maximum contaminant level for drinking water (0.01 mg As L(-1)). Four-year FWM Fe concentrations and runoff losses were greater (P < 0.05) from the high than from the low litter treatment and unamended control, and the 4-yr FWM P concentration from the low litter treatment (3.0 mg L(-1)) was greater than that from the unamended control (1.8 mg L(-1)). Since precipitation is temporally variable, evaluating runoff water quality in response to natural precipitation over several years is key to ascertaining the long-term impacts of surface-applied soil amendments like broiler litter.

Dredging of drainage ditches increases short-term transport of soluble phosphorus.

Managed drainage ditches are common in the midwestern United States. These ditches are designed to remove water from fields as quickly as possible, and sediment buildup necessitates dredging, to ensure adequate water removal. This laboratory study was conducted to determine the impact of ditch dredging on soluble phosphorus (P) transport. Ditch sediments were collected from a drainage ditch in northeastern Indiana immediately before and after dredging. The sediments were placed in a stream simulator, and stream water was loaded with 0.55 mM P for 5 d (adsorption experiment). Water was then removed, and "clean" water (no P added) was used for a desorption experiment, lasting 1 d. During the adsorption experiment, pre-dredged sediments were able to remove P from the water column quicker, and P concentrations 120 h after introduction of high P water were lower for the pre-dredged sediments (0.075 mM P) than the dredged sediments (0.111 mM P). During the desorption experiment, P was released to the water column slower in the pre-dredged treatment than the dredged treatment (instantaneous flux at t = 0 was 0.205 microM P h(-1) for pre-dredged and 0.488 microM P h(-1) for dredged). This occurred despite higher Mehlich 3-extractable P in the pre-dredged sediments than the dredged sediments. Equilibrium phosphorus concentrations (EPCo) were lower in the pre-dredged sediments during both adsorption and desorption experiments. Transport of soluble P immediately after dredging will likely increase in drainage ditches; however, dredging is a necessary management tool to ensure adequate discharge of water from surrounding fields.

Predicting dissolved phosphorus in runoff from manured field plots.

Dissolved inorganic P transport in runoff from agricultural soils is an environmental concern. Models are used to predict P transport but rarely simulate P in runoff from surface-applied manures. Using field-plot data, we tested a previously proposed model to predict manure P in runoff. We updated the model to include more data relating water to manure ratio to manure P released during water extractions. We verified that this update can predict P release from manure to rain using published data. We tested the updated model using field-plot and soil-box data from three manure runoff studies. The model accurately predicted runoff P for boxes, but underpredicted runoff P for plots. Underpredictions were caused by runoff to rain ratios used to distribute P into runoff or infiltration. We developed P distribution fractions from manure water extraction data to replace runoff to rain ratios. Calculating P distribution fractions requires knowing rainfall rate and times that runoff begins and rain stops. Using P distribution fractions gave accurate predictions of runoff P for soil boxes and field plots. We observed relationships between measured runoff to rain ratios and both P distribution fractions and a degree of error in original predictions, calculated as (measured runoff P/predicted runoff P). Using independent field-plot data, we verified that original underpredictions of manure runoff P can be improved by calculating P distribution fractions from measured runoff to rain ratios or adjusting runoff to rain ratios based on their degree of error. Future work should test the model at field or watershed scales and at longer time scales.

Phosphorus flux from bottom sediments in Lake Eucha, Oklahoma.

Phosphorus inputs into reservoirs include external sources from the watershed and internal sources from the reservoir bottom sediments. This study quantified sediment P flux in Lake Eucha, northeastern Oklahoma, USA, and evaluated the effectiveness of chemical treatment to reduce sediment P flux. Six intact sediment-water columns were collected from three sites in Lake Eucha near the reservoir channel at depths of 10 to 15 m. Three intact sediment and water columns from each site were incubated for 21 d at approximately 22 degrees C under aerobic conditions, and three were incubated under anaerobic conditions (N2 with 300 ppm CO2); sediment P flux was estimated over the 21 d for each core. The overlying water in the cores was bubbled with air for approximately 1 wk and then treated with aluminum sulfate (alum). The cores were incubated at approximately 22 degrees C for an additional 14 d under aerobic or anaerobic conditions, and sediment P flux after alum treatment was estimated for each core. Sediment P flux was approximately four times greater under anaerobic conditions compared with aerobic conditions. Alum treatment of the intact sediment-water columns reduced (8x) sediment P flux under anaerobic conditions. Internal P flux (1.03 and 4.40 mg m(-2) d(-1) under aerobic and anaerobic conditions, respectively) was greater than external P flux (0.13 mg m(-2) d(-1)). The internal P load (12 Mg yr(-1)) from reservoir bottom sediments was almost 25% of the external P load (approximately 48 Mg yr(-1)) estimated using a calibrated watershed model.

Evaluation of the phosphorus source component in the phosphorus index for pastures.

A phosphorus (P) index for pastures was developed to write nutrient management plans that determine how much P can be applied to a given field. The objectives of this study were to (i) evaluate and compare the P index for pastures, particularly the P source component, and an environmental threshold soil test P level by conducting rainfall simulations on contrasting soils under various management scenarios; and (ii) evaluate the P index for pastures on field-scale watersheds. Poultry litter was applied to 12 small plots on each of six farms based on either an environmental threshold soil test P level or on the P index for pastures, and P runoff was evaluated using rainfall simulators. The P index was also evaluated from two small (0.405 ha) watersheds that had been fertilized annually with poultry litter since 1995. Results from the small plot study showed that soil test P alone was a poor predictor of P concentrations in runoff water following poultry litter applications. The relationship between P in runoff and the amount of soluble P applied was highly significant. Furthermore, P concentrations in runoff from plots with and without litter applications were significantly correlated to P index values. Studies on pastures receiving natural rainfall and annual poultry litter applications indicated that the P index for pastures predicted P loss accurately without calibration (y = 1.16x - 0.23, r(2) = 0.83). These data indicate that the P index for pastures can accurately assess the risk of P loss from fields receiving poultry litter applications in Arkansas and provide a more realistic risk assessment than threshold soil test P levels.

Decreasing phosphorus runoff losses from land-applied poultry litter with dietary modifications and alum addition.

Phosphorus (P) losses from pastures fertilized with poultry litter contribute to the degradation of surface water quality in the United States. Dietary modification and manure amendments may reduce potential P runoff losses from pastures. In the current study, broilers were fed a normal diet, phytase diet, high available phosphorus (HAP) corn diet, or HAP corn + phytase diet. Litter treatments were untreated control and alum added at 10% by weight between flocks. Phytase and HAP corn diets reduced litter dissolved P content in poultry litter by 10 and 35%, respectively, compared with the normal diet (789 mg P kg(-1)). Alum treatment of poultry litter reduced the amount of dissolved P by 47%, while a 74% reduction was noted after alum treatment of litter from the HAP corn + phytase diet. The P concentrations in runoff water were highest from plots receiving poultry litter from the normal diet, whereas plots receiving poultry litter from phytase and HAP corn diets had reduced P concentrations. The addition of alum to the various poultry litters reduced P runoff by 52 to 69%; the greatest reduction occurred when alum was used in conjunction with HAP corn and phytase. This study demonstrates the potential added benefits of using dietary modification in conjunction with manure amendments in poultry operations. Integrators and producers should consider the use of phytase, HAP corn, and alum to reduce potential P losses associated with poultry litter application to pastures.

Water quality impacts of converting to a poultry litter fertilization strategy.

When improperly managed, land application of animal manures can harm the environment; however, limited watershed-scale runoff water quality data are available to research and address this issue. The water quality impacts of conversion to poultry litter fertilization on cultivated and pasture watersheds in the Texas Blackland Prairie were evaluated in this three-year study. Edge-of-field N and P concentrations and loads in surface runoff from new litter application sites were compared with losses under inorganic fertilization. The impact on downstream nutrient loss was also examined. In the fallow year with no fertilizer application, nutrient losses averaged 3 kg N ha(-1) and 0.9 kg P ha(-1) for the cultivated watersheds and were below 0.1 kg ha(-1) for the pasture watersheds. Following litter application, PO(4)-P concentrations in runoff were positively correlated to litter application rate and Mehlich-3 soil P levels. Following litter application, NO(3)-N and NH(4)-N concentrations in runoff were typically greater from cultivated watersheds, but PO(4)-P concentrations were greater for the pasture watersheds. Total N and P loads from the pasture watersheds (0.2 kg N ha(-1) and 0.7 kg P ha(-1)) were significantly lower than from the cultivated watersheds (32 kg N ha(-1) and 5 kg P ha(-1)) partly due to lower runoff volumes from the pasture watersheds. Downstream N and P concentrations and per-area loads were much lower than from edge-of-field watersheds. Results demonstrate that a properly managed annual litter application (4.5 Mg ha(-1) or less depending on litter N and P content) with supplemental N should supply necessary nutrients without detrimental water quality impacts.

Reducing phosphorus runoff from swine manure with dietary phytase and aluminum chloride.

Phosphorus (P) runoff from fields fertilized with swine (Sus scrofa) manure has been implicated in eutrophication. Dietary modification and manure amendments have been identified as best management practices to reduce P runoff from manure. This study was conducted to compare the effects of dietary modification and aluminum chloride (AlCl3) manure amendments on reducing P in swine manure and runoff. Twenty-four pens of nursery swine were fed either a normal diet or a phytase-amended diet. Each pen was connected to a separate manure pit, which was treated with AlCl3 to give final concentrations in the liquid manure of 0 (control), 0.25, 0.50, or 0.75% (v/v). Manure was collected and applied to plots cropped with tall fescue (Festuca arundinacea Schreb.), and simulated rainfall was applied at 50 mm h(-1), sufficient to generate a minimum of 30 min of continuous runoff. Samples of manure and runoff were analyzed for P and Al concentrations. Phytase reduced manure soluble reactive phosphorus (SRP) by 17%, while AlCl3 reduced manure SRP by as much as 73% compared with normal manure. Phosphorus runoff was reduced from 5.7 to 2.6 mg P L(-1) (a 53% reduction) using AlCl3. The mean SRP concentration in runoff from phytase diets without AlCl3 was 7.1 mg P L(-1) during the first rainfall simulation. When phytase and AlCl3 were used together, both manure SRP and P runoff were reduced more than if either treatment were used without the benefit of the other. Use of AlCl3 did not increase soluble Al in manure or Al lost in runoff. Results from this study indicate that producers should use dietary manipulation with phytase and AlCl3 manure amendments to reduce potential P losses from fields fertilized with swine manure.

Effect of aluminum chloride and dietary phytase on relative ammonia losses from swine manure.

Ammonia (NH3) losses from swine manure contribute to odor problems, decrease animal productivity, and increase the risk of acid rain deposition. This study was conducted to determine whether aluminum chloride (AlCl3) or dietary manipulation with phytase could decrease relative NH3 losses from swine manure. Twenty-four pens of nursery pigs were used in two trials, and the pigs were fed normal or phytase-supplemented (500 IU/kg) diets. Aluminum chloride was added to manure pits (1.9 x 1.2 x 0.5 m) under each pen at 0, 0.25, 0.50, or 0.75% (vol:vol) of final manure volume. Manure pH and NH3 losses (measured by relative NH3 flux) were determined twice weekly. The addition of AlCl3 at 0.75% decreased (P < 0.05) manure pH from 7.48 to 6.69. Phytase decreased (P < 0.05) manure pH to 7.07 compared with 7.12 in the normal diet manure. Aluminum chloride administered at 0.75% without phytase reduced (P < 0.05) relative NH3 losses 52% for the entire 6-wk period. Relative NH3 losses were decreased (P < 0.05) from 109 mg of NH3/(m2 x h) in pens containing pigs fed the normal diet without AlCl3 to 81 mg of NH3/(m2 x h) in pens housing pigs administered the phytase diet, a 26% reduction. When the phytase diet and 0.75% AlCl3 additions were used in combination, relative NH3 losses were reduced (P < 0.05) by 60% compared with pens of pigs fed the control diet without AlCl3. Decreases in manure pH were likely responsible for the observed reduction in NH3 losses. Multiple regression was performed with relative rates of NH3 losses as the dependent variable and rate of AlCl3 addition, diet, and manure pH as independent variables. The model was tested using a stepwise regression (P < 0.001), and results indicated that the most important factors determining NH3 losses were manure pH and diet. However, the contribution of AlCl3 cannot be discounted. When manure pH was regressed against AlCl3 and dietary phytase, AlCl3 levels accounted for 64% of the variation in manure pH (P < 0.001). Dietary manipulation with phytase and application of AlCl3 to manure are promising management practices for the reduction of NH3 from swine facilities.