Dissolved Reactive Phosphorus Concentrations Research Articles

Combined Gel Probes for the In Situ Determination of Dissolved Reactive Phosphorus in Porewaters and Characterization of Sediment Reactivity

Diffusive equilibrium in thin films (DET) and diffusive gradients in thin films (DGT) were applied in situ to obtain high spatial resolution dissolved reactive phosphorus (DRP) sediment porewater profiles in two lagoons of the Gippsland Lakes (SE Australia) during summer. Although the DRP depth profiles were different in each lake, highlighting the sensitivity of DRP to the redox state of the sediment spatial DRP variations obtained from DET and DGT showed striking similarities with depth in each lake. Comparison of DRP concentrations obtained from DGT and DET allows an assessment of the reactivity of the sediment. A dynamic numerical model of DGT-induced flux in sediments (DIFS) quantified reactivity kinetics. Sediment response time (Tc) related to sedimentary phosphorus resupply resulting from DGT-induced lowering of the porewater DRP concentration was calculated. Values of Tc ranged from 4128 to 183 400 s and from 55 to 149 400 s for Lakes Victoria and Wellington, respectively. These results indicate the limited capacity of the sediment to quickly resupply DRP to the porewater, especially in surface sediment which was always characterized by the highest Tc. Adsorption and desorption rate constants were also calculated from DIFS with values ranging from 2 x 10(-3) to 2 x 10(-2) day(-1) and from 0.3 to 21 day(-1) for Lake Victoria and from 2 x 10(-4) to 0.8 day(-1) and from 0.6 to 1558 day(-1) for Lake Wellington, respectively. Diffusive fluxes estimated from the in situ DRP gradient at the sediment-water interface by DET were 558 and 1.2 micromol m(-2) day(-1) in lakes Victoria and Wellington, respectively. Despite only a single measurement, these fluxes highlight a substantial contribution of P from the sediment to the water column in summer for Lake Victoria which is likely to contribute to the recurring blooms of blue-green algae. These calculated fluxes obtained with minimal sediment disturbance and high spatial resolution were substantially different (by a factor of 6-180) from other reported values using more conventional quantitative assessments such as diffusive fluxes (from core slicing) and benthic chambers.

A low-tech, low-cost passive sampler for the long-term monitoring of phosphate loads in rivers and streams

The concentration of dissolved reactive phosphorus (DRP) in rivers can change intermittently within minutes depending on the weather and water discharge (Q), or activities in the watershed. Accordingly, accurate estimation of the annual DRP load requires frequent sampling or even continuous monitoring, which is laborious and cost-intensive. We present the design and laboratory evaluation of a new, robust, low-cost, low-tech device based on passive samplers (P-traps). The traps use Fe-(oxy)hydroxide coated quartz sand as an adsorbent enclosed in a vertical grid of individual cells separated from the river water by filter membranes. They are inexpensive, easy to handle, resistant to repeated desiccation and immersion and exposable for several months. They permit estimation of discharge dependent time weighted average DRP concentrations (C-Q relationships) and annual P loads of rivers characterized by highly variable DRP concentrations with a relative accuracy of +/- 3%.

Increase in Phosphorus Losses from Grassland in Response to Olsen‐P Accumulation

The Olsen-P status of grazed grassland (Lolium perenne L.) swards in Northern Ireland was increased over a 5-yr period (March 2000 to February 2005) by applying different rates of P fertilizer (0, 10, 20, 40, or 80 kg P ha(-1) yr(-1)) to assess the relationship between soil P status and P losses in land drainage water and overland flow. Plots (0.2 ha) were hydrologically isolated and artificially drained to v-notch weirs, with flow proportional monitoring of drainage water and overland flow. Annually, the collectors for overland flow intercepted between 11 and 35% of the surplus rainfall. Single flow events accounted for up to 52% of the annual dissolved reactive phosphorus (DRP) load. The Olsen-P status of the soil influenced DRP and total phosphorus (TP) concentrations in land drainage water and overland flow. Annual TP loss was highly variable and ranged from 0.19 to 1.55 kg P ha(-1) yr(-1) for the plot receiving no P fertilizer and from 0.35 to 2.94 kg P ha(-1) yr(-1) for the plot receiving 80 kg P ha(-1) yr(-1). Despite the Olsen-P status in the soils ranging from 22 to 99 mg P kg(-1), after 5 yr of fertilizer P applications it was difficult to identify a clear Olsen-P concentration at which P losses increased. Any relationship was confounded by annual variability of hydrologic events and flows and by hydrologic differences between plots. Withholding P fertilizer for over 5 yr was not long enough to lower P losses or to have an adverse effect on herbage P concentrations.

Dissolved reactive phosphorus in large rivers of East Asia

Dissolved reactive phosphorus (DRP) concentrations in large pristine rivers of East Asia (370 samples) are reported and the relationship to lithology (phosphorites, igneous apatite-bearing deposits), relief, climate (precipitation, temperature), and population density are investigated. The DRP concentration and yield of 93% of our samples were distinctly low (<0.06–0.89 μM DRP and <0.0008–800 mol DRP/km2/year). The samples with relatively high DRP (∼7% of our samples) were most likely from point sources of human sewage rather than P-rich lithology. The principal component analyses using DRP, dissolved major elements, pH, Sr, and 87Sr/86Sr found DRP best grouped with dissolved Si and K. However, the correlation between DRP and dissolved Si is still not strong enough to justify using Si as a proxy of DRP export by chemical weathering. The large rivers draining the eastern Tibetan Plateau—the headwaters of the Mekong, Yangtze, and Yellow—together supplied 3.0 × 107 mol DRP/year, 7%, 3%, and 17% of those at mouths, respectively, and were not dominant source regions of DRP. The mouth values of the East Siberian rivers were especially low and this was due to multiple factors, e.g., low precipitation and sparse population. Stepwise regression of various parameters like precipitation, temperature, runoff, population density and relief indicated that the concentrations were not affected by any single factor, but precipitation and secondarily population density explained up to 44% of the variability in the DRP yield of the East Asian rivers.

Nutrient flux in storm water runoff and baseflow from managed turf

The urban landscape is comprised of many land uses, none more intensively managed than turfgrass; however, quantification of nutrient losses from specific land uses within urban watersheds, specifically golf courses is limited. Nitrate (NO 3-N) and dissolved reactive phosphorus (DRP) were measured on a golf course in Austin, TX, USA from April 1, 1998 to March 31, 2003. NO 3-N and DRP concentrations measured in storm flow were significantly greater exiting the course compared to those entering the course. Significant differences were also measured in baseflow NO 3-N concentrations. The measured loading from the course was 4.0 kg NO 3-N ha −1 yr −1 (11% of applied) and 0.66 kg DRP ha −1 yr −1 (8% of applied). The resulting concentrations contributed by the course were 1.2 mg L −1 NO 3-N and 0.2 mg L −1 DRP. At these levels, NO 3-N poses minimal environmental risk. However, the DRP concentration is twice the recommended level to guard against eutrophication.

Sediment nutrient flux in a coastal lake impacted by diverted Mississippi River water

The internal nutrient load from bottom sediment to the water column of a Louisiana Barataria Basin lake (Lake Cataouatche) receiving diverted Mississippi River water was determined. Dissolved reactive phosphorus (DRP), ammonium (NH4-N) and nitrate (NO3-N) flux from sediment to water column were measured. The DRP flux averaged−0.22 mg m−2 d−1 under aerobic water column conditions, as compared with that 3.29 mg m−2 d−1 under anaerobic conditions. The average NH4-N released under anaerobic conditions (1.42 mg m−2 d−1) was significantly greater than rates under aerobic conditions (−0.02 mg m−2 d−1), indicating a strong relationship between nutrient flux and oxygen availability in the water column. The average NO3-N flux was 2.13 mg m−2 d−1 under aerobic conditions as compared with−0.24 mg m−2 d−1 under anaerobic conditions in the sediment–water column. When the water column maintained under anaerobic conditions was switched to aerobic conditions, the DRP, NH4-N, and NO3-N concentrations in overlying water decreased rapidly over a short period of time. The mean annual internal DRP and NH4-N load from the sediment to the overlying water was estimated to be 69.26 and 29.9 tonnes (Mg) yr−1 respectively, which represents a significant portion of the total nutrient load to the Lake. Results demonstrate that the internal flux of nutrients from sediments can contribute a significant portion of the total nutrient load to the water column and should be considered in decisions on impact of nutrient in diverted Mississippi River on water quality of Barataria Basin.

Streambed Sediment Geochemical Controls on In-Stream Phosphorus Concentrations during Baseflow

A spatially extensive geochemical data set of stream water and bed sediment composition across the Tamar catchment in south-west England was analysed to identify the key bed sediment properties that control the in-stream dissolved reactive phosphorus (DRP) concentrations during baseflow conditions. Linear regression analysis of the streamwater DRP concentrations and the distribution coefficient Kd for DRP revealed that the former is positively correlated with total SiO2 and Al2O3, and negatively correlated with K2O. The primary control on these major element distributions is the dominant bedrock geology. The data suggest that streamwater DRP concentrations are mainly controlled by adsorption to clay minerals. Where P concentrations in streamwater were considerably elevated by inputs from point sources, DRP concentrations are also controlled by precipitation of hydroxyapatite.

Phosphorus and Nitrogen in Rainfall Simulation Runoff after Fresh and Composted Beef Cattle Manure Application

Fresh beef cattle (Bos taurus) manure has traditionally been applied to cropland in southern Alberta, but there has been an increase in application of composted manure to cropland in this region. However, the quality of runoff under fresh manure (FM) versus composted manure (CM) has not been investigated. Our objective was to compare runoff quality under increasing rates (0, 13, 42, 83 Mg ha(-1) dry wt.) of FM and CM applied for two consecutive years to a clay loam soil cropped to irrigated barley (Hordeum vulgare L.). We determined total phosphorus (TP), particulate phosphorus (PP), dissolved reactive phosphorus (DRP), total nitrogen (TN), NH4-N, and NO3-N concentrations and loads in runoff after one (1999) and two (2000) applications of FM and CM. We found significantly (P < or = 0.05) higher TP, DRP, and NH4-N concentrations, and higher DRP and TN loads under FM than CM after 2 yr of manure application. The TP loads were also higher under FM than CM at the 83 Mg ha(-1) rate in 2000, and DRP loads were higher for FM than CM at this high rate when averaged over both years. Application rate had a significant effect on TP and DRP concentrations in runoff. In addition, the slope values of the regressions between TP and DRP in runoff versus application rate were considerably higher for FM in 2000 than for FM in 1999, and CM in both 1999 and 2000. Significant positive relationships were found for TP and DRP in runoff versus soil Kelowna-extractable P and soil water-extractable P for FM and CM in 2000, indicating that interaction of runoff with the soil controlled the release of P. Total P and DRP were the variables most affected by the treatments. Overall, our study found that application of CM rather than FM to cropland may lower certain forms of P and N in surface runoff, but this is dependent on the interaction with year, application rate, or both.

Growth of the diatom Chaetoceros calcitrans in sediment extracts from Artemia franciscana ponds at different concentrations of nitrogen and phosphorus

This study was carried out with the aim to optimize the growth of the diatom Chaetoceros calcitrans ( C. calcitrans) to feed Artemia franciscana. This is based on management of both quantities and ratios of nutrients dissolved in the water column, especially nitrogen (N) and phosphorus (P). To this end, algae were inoculated in media prepared from the extracts of Artemia pond sediments to relate their growth with the availability of N and P present in these extracts. Algal responses to different levels of dissolved inorganic nitrogen (DIN), dissolved reactive phosphorus (DRP) and to widely varying DIN:DRP ratios in the water column were examined by adding inorganic N (6.6–76 mg N L − 1 ) and P (0.01–0.2 mg P L − 1 ) to the media at different combinations. In all media, inoculation of algae at a density of 50 × 10 3 cells mL − 1 resulted in an exhaustion of DRP after five days. Adding inorganic P to the media stimulated algae to assimilate more N and increased algal densities ( R 2 = 0.70, P < 0.001) and biomass ( R 2 = 0.68, P < 0.001). In contrast, adding inorganic N decreased algal production. The densities of algae decreased logarithmically when DIN:DRP ratios increased from 50 to 910. Below DIN:DRP 150, the densities and biomass of algae were strongly dependent on the initial concentrations of DRP. When DIN:DRP ratios exceed 150, algal densities and biomass were constantly low, regardless the availability of DRP. In these media, supplying DRP to reach concentrations above 0.06 mg P L − 1 , while maintaining DIN:DRP below 150, is suitable for the growth of C. calcitrans.

Sediment and Phosphorus Transport in Irrigation Furrows

Sediment and phosphorus (P) in agricultural runoff can impair water quality in streams, lakes, and rivers. We studied the factors affecting P transfer and transport in irrigated furrows in six freshly tilled fallow fields, 110 to 180 m long with 0.007 to 0.012 m m-1 slopes without the interference of raindrops or sheet flow that occur during natural or simulated rain. The soil on all fields was Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids). Flow rate, sediment concentration, and P concentrations were monitored at four, equally spaced locations in each furrow. Flow rate decreased with distance down the furrow as water infiltrated. Sediment concentration varied with distance and time with no set pattern. Total P concentrations related directly to sediment concentrations (r2=0.75) because typically >90% of the transported P was particulate P, emphasizing the need to control erosion to reduce P loss. Dissolved reactive phosphorus (DRP) concentrations decreased with time at a specific furrow site but increased with distance down the furrow as contact time with soil and suspended sediment increased. The DRP concentration correlated better with sediment concentration than extractable furrow soil P concentration. However, suspended sediment concentration tended to not affect DRP concentration later in the irrigation (>2 h). These results indicate that the effects of soil P can be overshadowed by differences in flow hydraulics, suspended sediment loads, and non-equilibrium conditions.

Corn Residue Level and Manure Application Timing Effects on Phosphorus Losses in Runoff

Growing interest in corn (Zea mays L.) silage utilization on Wisconsin dairy farms may have implications for nutrient losses from agricultural lands. Increasing the silage cutting height will increase residue cover and could reduce off-site migration of sediments and associated constituents compared with conventional silage harvesting. We examined the effects of residue level and manure application timing on phosphorus (P) losses in runoff from no-till corn. Treatments included conventional corn grain (G) and silage (SL; 10- to 15-cm cutting height) and nonconventional, high-cut (60-65 cm) silage (SH) subjected to different manure application regimes: no manure (N) or surface application in fall (F) or spring (S). Simulated rainfall (76 mm h(-1); 1 h) was applied in spring and fall for two years (2002-2003), runoff from 2.0- x 1.5-m plots was collected, and subsamples were analyzed for dissolved reactive phosphorus (DRP), total phosphorus (TP), and P mass distribution in four particle size classes. Total P and DRP loads were inversely related to percent residue cover, but both TP and DRP concentrations were unaffected by residue level. Manure application increased DRP concentrations in spring runoff by two to five times but did not significantly affect DRP loads, since higher concentrations were offset by lower runoff volumes. Spring manure application reduced TP loads in spring runoff by 77 to 90% compared with plots receiving no manure, with the extent of reductions being greatest at the lower residue levels (<24%). The TP concentration in sediments increased as particle size decreased. Manure application increased the TP concentration of the 0- to 2-microm fraction by 79 to 125%, but elevated the 2- to 10- and 10- to 50-microm fractions to a lesser extent. Recent manure additions were most influential in enriching transported sediments with P. By itself, higher residue cover achieved by high-cutting silage was often insufficient to lower P losses; however, the combination of manure application and higher residue levels significantly reduced P losses from corn fields harvested for silage.

OPTIMIZATION OF PHOSPHORUS PARTITIONING IN DAIRY MANURE USING CHEMICAL ADDITIVES WITH A MECHANICAL SOLIDS SEPARATOR

The use of liquid aluminum sulfate (alum) and a cationic polymer to precipitate soluble phosphorus, measuredas dissolved reactive phosphorus (DRP), from dairy manure was investigated in conjunction with a mechanical screw presssolids separator. The ability to partition phosphorus (P) into the recovered solids would increase the feasibility of transportingP off the farm. Initial settling studies were conducted using Imhoff cones to determine the effectiveness of aluminum (Al) toP molar ratios of 2.5:1, 5:1, and 7.5:1. In the Imhoff cone tests, the DRP concentration in the treated bulk liquid was 68%,95%, and 98% less than the control, respectively. For the mechanical separator tests, alum was added at a molar ratio of Alto P (measured as DRP, but converted to an elemental P equivalency for the ratio calculations) of 5.5:1, and alum plus acationic polymer was tested with the alum added at an Al to P molar ratio of 7.5:1. The DRP concentrations in the manureafter alum amendment at the 5.5:1 Al:P ratio (and prior to processing in the separator) and in the press liquor were 52% lessthan prior to alum amendment. The total phosphorus (TP) in the press liquor was not affected by alum addition because thealuminum phosphate floc remained with the press liquor when alum alone was added. With the addition of alum at a 7.5:1Al:P ratio in conjunction with cationic polymer at a rate of 55.5 mg L-1, the DRP concentration in the press liquor was reducedby 96%. When compared to the control, waste amended with alum and polymer had 82% less TP in the press liquor, whichindicates that P was partitioned into the press cake. This combined alum/polymer treatment also resulted in a 36% reductionin TS and a 71% reduction in chemical oxygen demand (COD) in the press liquor when compared to the control. Polymeraddition also increased the dry mass capture efficiency of the solid separator to 81.8% compared to 65.5% in the control,but the press liquor flow rate was reduced by 81%. The combined retail cost for alum and polymer addition at the above ratesis estimated to be $2.63 per 1000 L of treated manure slurry. The results indicate that a cationic polymer used in conjunctionwith alum amendment can effectively partition P into the press cake during mechanical solids separation.

Phytase Supplementation and Reduced‐Phosphorus Turkey Diets Reduce Phosphorus Loss in Runoff following Litter Application

Concerns about regional surpluses of manure phosphorus (P) leading to increased P losses in runoff have led to interest in diet modification to reduce P concentrations in diets. The objectives of this study were to investigate how dietary P amendment affected P concentrations in litters and P losses in runoff following land application. We grew two flocks of turkeys on the same bed of litter using diets with two levels of non-phytate phosphorus (NPP), with and without phytase. The litters were incorporated into three soils in runoff boxes at a plant-available nitrogen (PAN) rate of 168 kg PAN/ha, with runoff generated on Days 1 and 7 under simulated rainfall and analyzed for dissolved reactive phosphorus (DRP) and total P. Litters were analyzed for water-soluble phosphorus (WSP) and total P, while soils in the runoff boxes were analyzed for WSP and Mehlich-3 phosphorus (M3-P). Formulating diets with lower NPP and phytase both decreased litter total P. Phytase had no significant effect on litter WSP at a 1:200 litter to water extraction ratio, but decreased WSP at a 1:10 extraction ratio. Using a combination of reducing NPP fed and phytase decreased the total P application rate by up to 38% and the P in surplus of crop removal by approximately 48%. Reducing the NPP fed reduced DRP in runoff from litter-amended soils at Day 1, while phytase had no effect on DRP concentrations. Increase in soil M3-P was dependent on total P applied, irrespective of diet. Reducing overfeeding of NPP and utilizing phytase in diets for turkeys should decrease the buildup of P in soils in areas of intensive poultry production, without increasing short-term concerns about dissolved P losses.

Phosphorus export dynamics from two Swiss grassland catchments

Phosphorus (P) export from agricultural catchments is often event-driven and variable in time. Accordingly, a proper monitoring requires high-temporal resolution sampling during flow events. We report on a comparative study on the P export dynamics from two grassland catchments in Switzerland, where concentrations of dissolved reactive Phosphorus (DRP) have been monitored at a high temporal resolution for periods of 1.2 and 5 y, respectively. The data set is complemented by measurements on total P (TP), total dissolved P (TDP) and particulate P (PP) obtained from routine sampling ongoing since 1984 in both catchments. In one area, the high-temporal resolution monitoring revealed a pattern of the P export dynamic as expected from other studies. During flow events DRP concentrations usually increased significantly exceeding 1000 mg DRP m −3 during peak flow, while the values remained low between 20 and 100 mg DRP m −3 at base flow. This pattern was partially confirmed in the second catchment. The expected pattern was observed in 1998 and 1999 but was partially replaced by a new one for the following years. In the growing season, DRP only weakly increased with flow rate or remained almost constant. During flow events values larger than 300–400 mg DRP m −3 were rare. In contrast to these relatively low peak flow concentrations, high values (200–300 mg m −3) were recorded at base flow during the years 2000–2002. During the same period, DRP concentrations exhibited strong daily oscillations. Independent sampling and analytical control measurements verify the findings. Point sources like leaks from manure tanks could be ruled out based on the ammonia measurements. We suggest that biogeochemical processes within the brook are responsible for this change in the P export dynamics. Despite these changes in the pattern of the P export dynamic and ecological measures implemented on the farms no significant effect on the annual P loads could be observed during the last 10 years.

Particulate Phosphorus Transport within Stream Flow of an Agricultural Catchment

There is interest in quantifying phosphorus (P) loss from intensively grazed dairy landscapes to identify key pathways and target remediation methods. The Bog Burn drains a dairying catchment in Southland, New Zealand, and has been monitored at fortnightly intervals over a 12-mo period at four sites for suspended sediment (SS), dissolved reactive phosphorus (DRP), and total phosphorus (TP). Time-integrated samplers, deployed at 0.6 median water depth at each site (calculated from previous year's flow data), collected sediment samples, which were analyzed for SS, bioavailable phosphorus (BAP), and TP. Mean concentrations of DRP and TP in stream flow and BAP and TP in sediment were generally highest in summer or autumn (0.043 mg DRP L(-1), 0.160 mg TP L(-1), 173 mg BAP kg(-1), 2228 mg TP kg(-1)) and lowest in winter or spring (0.012 mg DRP L(-1), 0.034 mg TP L(-1), 6 mg BAP kg(-1), 711 mg TP kg(-1)), while loads were highest in winter. Analysis of (137)Cs concentrations in trapped sediment, topsoil, subsoil, and stream bed and bank sediment indicated that trapped sediment was derived from topsoil and entered the stream either through tile drainage or, to a lesser extent, overland flow. Because concentrations of DRP and TP in stream flow are in excess of recommended limits for good water quality (>0.01 mg DRP L(-1), 0.033 mg TP L(-1)), management should focus on the topsoil and specifically on decreasing P loss via tile drainage. This is best achieved by decreasing soil Olsen P concentrations, especially because, on average, Olsen P concentrations in the catchment were above the agronomic optimum.

Dissolution of phosphate in a phosphorus-enriched ultisol as affected by microbial reduction.

Phosphorus dissolution often increases as soils become more reduced, but the mechanisms are not fully understood. The objectives of this research were to determine rates and mechanisms of P dissolution during microbial reduction of a surface soil from the North Carolina Coastal Plain. Duplicate suspensions of silt + clay fractions from a Cape Fear sandy clay loam (fine, mixed, semiactive, thermic Typic Umbraquult) were reduced in a continuously stirred redox reactor for 40 d. We studied the effects of three treatments on P dissolution: (i) 2 g dextrose kg(-1) solids added as a microbial carbon source at time 0 d; (ii) 2 g dextrose kg(-1) solids split into three additions at 0, 12, and 26 d; and (iii) no added dextrose. After 40 d of reduction, concentrations of dissolved reactive phosphorus (DRP) were similar for all treatments and increased up to sevenfold from 1.5 to 10 mg L(-1). The initial rate of reduction and dissolution of DRP was significantly greater for the 0-d treatment. A linear relationship (R(2) = 0.79) was found between DRP and dissolved organic carbon (DOC). Dissolved Fe and Al and pH increased, suggesting the formation of aqueous Fe- and Al-organic matter complexes. Separate batch experiments were performed to study the effects of increasing pH and citrate additions on PO(4) dissolution under aerobic conditions. Increasing additions of citrate increased concentrations of DRP, Fe, and Al, while increasing pH had no effect. Results indicated that increased dissolved organic matter (DOM) during soil reduction contributed to the increase in DRP, perhaps by competitive adsorption or formation of aqueous ternary DOM-Fe-PO(4) or DOM-Al-PO(4) complexes.

Surface runoff losses of phosphorus from Virginia soils amended with turkey manure using phytase and high available phosphorus corn diets.

Many states have passed legislation that regulates agricultural P applications based on soil P levels and crop P uptake in an attempt to protect surface waters from nonpoint P inputs. Phytase enzyme and high available phosphorus (HAP) corn supplements to poultry feed are considered potential remedies to this problem because they can reduce total P concentrations in manure. However, less is known about their water solubility of P and potential nonpoint-source P losses when land-applied. This study was conducted to determine the effects of phytase enzyme and HAP corn supplemented diets on runoff P concentrations from pasture soils receiving surface applications of turkey manure. Manure from five poultry diets consisting of various combinations of phytase enzyme, HAP corn, and normal phytic acid (NPA) corn were surface-applied at 60 kg P ha(-1) to runoff boxes containing tall fescue (Festuca arundinacea Schreb.) and placed under a rainfall simulator for runoff collection. The alternative diets caused a decrease in manure total P and water soluble phosphorus (WSP) compared with the standard diet. Runoff dissolved reactive phosphorus (DRP) concentrations were significantly higher from HAP manure-amended soils while DRP losses from other manure treatments were not significantly different from each other. The DRP concentrations in runoff were not directly related to manure WSP. Instead, because the mass of manure applied varied for each treatment causing different amounts of manure particles lost in runoff, the runoff DRP concentrations were influenced by a combination of runoff sediment concentrations and manure WSP.

Phosphorus runoff from incorporated and surface-applied liquid swine manure and phosphorus fertilizer.

Excessive fertilization with organic and/or inorganic P amendments to cropland increases the potential risk of P loss to surface waters. The objective of this study was to evaluate the effects of soil test P level, source, and application method of P amendments on P in runoff following soybean [Glycine max (L.) Merr.]. The treatments consisted of two rates of swine (Sus scrofa domestica) liquid manure surface-applied and injected, 54 kg P ha(-1) triple superphosphate (TSP) surface-applied and incorporated, and a control with and without chisel-plowing. Rainfall simulations were conducted one month (1MO) and six months (6MO) after P amendment application for 2 yr. Soil injection of swine manure compared with surface application resulted in runoff P concentration decreases of 93, 82, and 94%, and P load decreases of 99, 94, and 99% for dissolved reactive phosphorus (DRP), total phosphorus (TP), and algal-available phosphorus (AAP), respectively. Incorporation of TSP also reduced P concentration in runoff significantly. Runoff P concentration and load from incorporated amendments did not differ from the control. Factors most strongly related to P in runoff from the incorporated treatments included Bray P1 soil extraction value for DRP concentration, and Bray P1 and sediment content in runoff for AAP and TP concentration and load. Injecting manure and chisel-plowing inorganic fertilizer reduced runoff P losses, decreased runoff volumes, and increased the time to runoff, thus minimizing the potential risk of surface water contamination. After incorporating the P amendments, controlling erosion is the main target to minimize TP losses from agricultural soils.

The influence of the North Atlantic Oscillation on the physical, chemical and biological characteristics of four lakes in the English Lake District

Summary1. Thirty‐six years of winter meteorological and limnological measurements from four lakes in the English Lake District are analysed and related to variations in the North Atlantic Oscillation (NAO). Winter weather conditions were strongly influenced by the NAO with mild, wet winters being associated with strongly positive values of the NAO index (NAOI).2. Lake surface and bottom temperatures were strongly positively correlated with the NAOI, with the highest correlations being recorded in the shallower lakes.3. Variations in the NAOI also had a significant effect on the winter concentration of nitrate. In all the lakes, there was a significant negative correlation between the NAOI and the detrended winter concentration of nitrate. The key driving variable was the local air temperature, which appeared to limit the quantity of nitrate reaching the lake by increasing the amount assimilated in the surrounding catchment in mild winters.4. Dissolved reactive phosphorus (DRP) concentrations were not significantly correlated with the NAOI in the two larger basins but significant positive correlations were recorded in the two smaller lakes. The key driving variable was the local rainfall with higher DRP concentrations being recorded after heavy rain in the lakes with a short retention time.5. The NAOI‐related changes in rainfall also influenced the phytoplankton. In wet winters the concentration of chlorophyll in the two smaller lakes with the shortest retention time was lower and the spring growth of Asterionella formosa was delayed in the smallest lake.6. These differential responses demonstrate how the large‐scale effects associated with the NAO can be ‘filtered’ by the physical characteristics of a particular site.

Dissolved reactive phosphorus in a Calcaric Fluvisol as affected by the addition of agricultural wastes

Abstract. Land application of organic wastes can result in the accumulation of available soil phosphorus (P) and in an increase risk of eutrophication of surface and shallow groundwaters. We conducted laboratory experiments to examine the effect of waste application on the concentration of dissolved reactive phosphorus (DRP) in 1:5 soil to 0.005 m CaCl2 suspensions. Ten organic wastes, of which eight were mature composts, were applied to a P‐rich Calcaric Fluvisol at rates ranging from 0 to 10% of soil by weight, and the difference in DRP concentration between suspensions containing waste and the untreated control (ΔDRP) was measured over a period of 300 days. In half of the suspensions of each waste–soil combination, 80 mg P (as KH2PO4) kg−1 soil was applied at day 14. Values of ΔDRP were generally positive, but a significant number of negative values were also recorded for some wastes and application rates, particularly at later sampling times if inorganic P had been added. Regression analyses revealed that ΔDRP (i) increased with increasing soluble reactive P at all times and (ii) increased in the short term, but decreased in the long term with increasing water soluble organic carbon in the waste. The fact that ΔDRP was sometimes negative for some waste types suggests that application of organic waste to soil does not necessarily increase eutrophication risks caused by soil P losses.