Release Of Soluble Reactive P Research Articles

Trade-offs between nitrogen and phosphorus removal with floodplain remediation in agricultural streams

To improve water quality and reduce instream erosion, floodplain remediation along agricultural streams can provide multiple ecosystem services through biogeochemical and fluvial processes. During floodplain inundation, longer water residence time and periodic anoxic conditions can lead to increased nitrogen (N) removal through denitrification but also mobilization of phosphorus (P), impeding overall water quality improvements. To investigate the capacity for N and P processing in remediated streams, we measured potential denitrification and nitrous oxide production and yields together with potential P desorption and P fractions in floodplain and stream sediments in ten catchments in Sweden. Sediment P desorption was measured as equilibrium P concentration, using P isotherm incubations. Denitrification rates were measured with the acetylene inhibition method. Sediment nutrient process rates were combined with hydrochemical monitoring along remediated streams and their paired upstream control reaches of trapezoidal shape to determine the impact of floodplains on water quality. The correlation between floodplain denitrification rates and P desorption (r = 0.53, p = 0.02) revealed a trade-off between soluble reactive P (SRP) and nitrate removal, driven by stream water connectivity to floodplains. Nitrous oxide production was not affected by differences in P processing, but nitrous oxide yields decreased with higher denitrification and P desorption. The release of SRP from floodplains (0.03 ± 0.41 mg P kg−1 day−1) was significantly lower than from trapezoidal stream banks (0.38 ± 0.37 mg P kg−1 day−1), predicted by long-term SRP concentrations in stream water and floodplain inundation frequency. The overall impact of SRP release from floodplains on stream SRP concentrations in remediated reaches was limited. However, the remediated reaches showing increased stream SRP concentrations were also frequently inundated and had higher labile P content and coarse soil texture in floodplain sediments. To fully realize the potential for water quality improvements with constructed floodplains in agricultural streams, the promotion of denitrification through increased inundation should be balanced against the risk of P release from sediments, particularly in streams with high SRP inputs.

Characterization of nitrogen and phosphorus at the ice-water-sediment interface and the effect of their migration on overlying water quality in Daihai Lake (China) during the freezing period

Approximately one-third of the year, Daihai Lake experiences freezing conditions. During this period, the primary mechanisms that impact the quality of the lake water quality include the freezing of nutrients by the ice sheet and the migration of nutrients between the ice, water, and sediment. The present investigation involved the collection of samples of ice, water, and sediment, followed by the utilization of the thin film gradient diffusion (DGT) technique to and explore the distribution and migration of diverse nitrogen (N) and phosphorus (P) forms at the interface of ice, water and sediment. The findings indicate that the freezing process led to the precipitation of ice crystals, which in turn caused the migration of a significant proportion (28–64 %) of nutrients to the subglacial water. The predominant constituents of N and P in subglacial water, were NO3−-N and PO43−-P, which constituted 62.5–72.5 % of total N (TN) and 53.7–69.4 % of total P(TP). Respectively, with increasing depth, the TN and TP of sediment interstitial water increased. The sediment in the lake acted as a source of PO43−-P and NO3−-N while acting as a sink or NH4+-N. Soluble reactive P (SRP) flux and NO3−-N flux were responsible for 76.5 % and 2.5 % of the P and N present in the overlying water. Additionally, it was observed that 60.5 % of the NH4+-N flux in the overlying water was absorbed and subsequently deposited in the sediment. The presence of soluble and active P in the ice sheet could play a crucial role in the regulation of sediment release of both SRP and NH4+-N. Additionally, the presence of high nutritional salts and the concentration of nitrate nitrogen in the overlying water would certainly increase the pressure of the water environment. Endogenous contamination must be urgently controlled.

Saltwater intrusion affects nitrogen, phosphorus and iron transformations under oxic and anoxic conditions: an incubation experiment

Low-lying coastal ecosystems are rapidly salinizing due to sea level rise and associated saltwater intrusion (SWI). In agricultural soils, SWI can alter biogeochemical cycling of key nutrients such as nitrogen (N), phosphorus (P), and iron (Fe). The main objective of this study was to quantify the amount of nitrate–N (NO3–N), ammonium–N (NH4–N), soluble reactive P (SRP), and total dissolved iron (TDFe) released from agricultural soils undergoing SWI to determine their potential loss to downstream waterways. Agricultural soils were incubated for 0, 15, and 30 days (under oxic and anoxic conditions) with various salt solution combinations of sodium chloride (NaCl), sodium sulfate (Na2SO4), calcium sulfate (CaSO4), and Instant Ocean® to mimic (1) different ionic constituents of saltwater at different ionic strengths and (2) the presence or absence of gypsum, a soil amendment, through the addition of CaSO4. We also included a set of incubations treated with deionized water as a no ionic strength control (0.00 M). To increase statistical power, we grouped individual salt treatments based on our initial hypotheses at the end of the incubation period (day 30) to determine the effects of high (0.26–0.28 M) and low (0.03–0.04 M) ionic strength on inorganic N release and combinations of Ca and SO42− additions on SRP release to microcosm soil solution. Calcium additions decreased SRP release relative to saltwater that contained only NaCl additions under oxic and anoxic conditions. Additionally, high ionic strength treatments, which were about 7 times the ionic strength of low ionic strength treatments, released two times as much NH4–N to the soil solution, which suggests a non-linear relationship between ionic strength and NH4–N release. At day 30, anoxic microcosm soils treated with Instant Ocean® to simulate 15 parts per thousand seawater (ionic strength 0.26 M) released significantly more NH4–N (by 782 times), SRP (by 6 times), and TDFe (by 197 times) to the soil solution than oxic microcosm soils (P < 0.05). This treatment was designed to reflect a field inundated by brackish seawater for almost a month, which is representative of conditions on farm fields undergoing SWI. Under these anoxic conditions, as much as 22% of bioavailable soil P (as SRP) and 45% of total inorganic N (as NH4–N) could be released to overlying water when inundated with saltwater. Our work indicates that the influx of salts and inundation of SWI-affected farm fields could lead to a large export of N and P from agricultural soils and potentially affect downstream water quality.

Combined use of calcium nitrate, zeolite, and anion exchange resin for controlling phosphorus and nitrogen release from sediment and for overcoming disadvantage of calcium nitrate addition technology.

Ca(NO3)2 addition has proved to have a high potential to immobilize internal phosphorus (P) in sediments; however, it cannot effectively stop the release of ammonium-nitrogen (NH4+-N) from sediments into overlying waters (OL-waters). Additionally, the addition of Ca(NO3)2 alone has high risk of nitrate-nitrogen (NO3--N) releasing into OL-waters. To overcome the shortcoming of the Ca(NO3)2 addition method, we reported an integrated method, i.e., a combined method based on Ca(NO3)2 injection, zeolite capping, and anion exchange resin (AERN)-contained floating system suspending (Ca(NO3)2/zeolite/AERN). The effectiveness and mechanism of the Ca(NO3)2/zeolite/AERN method for simultaneously controlling the release of soluble reactive P (SRP) and NH4+-N were investigated, and the NO3--N releasing risk of this method was evaluated. It was found that the joint use of Ca(NO3)2 injection, zeolite capping, and AERN-contained floating system suspending not only could effectively suppress the release of SRP and NH4+-N from sediments into OL-waters simultaneously, but also had much less risk of NO3--N releasing into OL-waters as compared to the single Ca(NO3)2 injection method and the combined Ca(NO3)2/zeolite method. The inhibition of the reductive dissolution of the P-bound Fe(III) oxides/hydroxides by the presence of nitrate and the adsorption of ammonium on the zeolite played very important roles in the interception of SRP and NH4+-N releasing into OL-waters by the Ca(NO3)2/zeolite/AERN method. After the sediment remediation using the Ca(NO3)2/zeolite/AERN approach, the increase in the content of residual P in the sediment layer of 0-50mm, the decrease of mobile P in the sediment layer of 0-10mm, and the increased NH4+-N adsorption capacity for the sediment layer of 0-10mm would be conductive to the interception of SRP and NH4+-N liberation in the long run. Results of this research suggest a promising application potential of the Ca(NO3)2/zeolite/AERN method in the simultaneous control of the release of SRP and NH4+-N from sediments.

Utilization of zirconium-modified granular zeolite as capping and mixing materials to suppress phosphorus release from sediment in landscape water body

A zirconium-modified granular zeolite (ZMGZ) was created and investigated for the suppression of the internal P loading in shallow landscape water bodies in this study. Results showed that the as-synthesized ZMGZ possessed high phosphate sorption capacity with a Langmuir maximum monolayer uptake capacity of 6.87 mg PO43−/g. Capping of landscape water body sediments with ZMGZ reduced the releasing rate of soluble reactive P (SRP) from the sediments into the overlying water, and it significantly reduced the SRP releasing rate under anoxic condition. Furthermore, the sediment capping decreased the pore water SRP concentration, and it was difficult for most of P trapped by the ZMGZ covering layer to be re-released into the water column. When the ZMGZ in the covering layer was mixed with the sediment, the ZMGZ became a sediment amendment. Mixing of landscape water body sediments with ZMGZ also resulted in the reduction of the SRP concentrations in the overlying and pore waters under the conditions of low and high dissolved oxygen, and it was also hard for most of P adsorbed by the added ZMGZ to be released back into the water column. Additionally, the addition of sediments with ZMGZ led to the decrease of the amounts of mobile and bioavailable P in the sediments. To sum up, we conclude that the capping/mixing combination method, which involves sediment capping with ZMGZ at first and then gradual mixing of ZMGZ with sediment via various natural disturbances (e.g., physical disturbance and bioturbation), is a very promising strategy for inhibiting the release of SRP from shallow landscape water body sediments into the overlying water.

Contrasting exchanges of nitrogen and phosphorus across the sediment–water interface during the drying and re-inundation of littoral eutrophic sediment

High water level fluctuations (WLFs) lead to periodic drying and re-inundation of sediments in the littoral area of eutrophic lakes. In this study, a series of littoral sediment cores were dried for different periods (5–30 d) and rewetted for 48 h. The sediment cores that dried for 30 d were then re-inundated for 90 d. The exchanges of nitrogen (N) and phosphorus (P) across the sediment–water interface (SWI) and the mechanisms were studied. The results showed that ammonium nitrogen (NH4+–N) fluxes increased after 5–25 d of drying, which was followed by an obvious decrease after 30 d of drying. The decreased NH4+–N fluxes remained at low levels during the 90 d re-inundation period. The soluble reactive P (SRP) fluxes decreased significantly after 15 d of drying. However, further re-inundation increased the SRP fluxes to their initial levels. The decreased water content and porosity, the oxidation of the sediment during drying, and the associated transformations of the N and P fractions in the sediment from drying to re-inundation influenced the exchanges of NH4+–N and SRP across the SWI. The decrease of labile NH4+–N in the sediment during drying was non-reversible, while the transformations between redox sensitive P (Fe-P) and aluminum-bound P were more likely to be reversible from drying to re-inundation. The increase of Fe-P during drying and dissolution of Fe-P during the re-inundation were responsible for the development of SRP fluxes from drying to re-inundation. Therefore, the periodic drying and re-inundation of the littoral eutrophic sediments reduced the release of NH4+–N but accelerated the release of SRP from the sediment. This should be given more consideration for the remediation and management of eutrophication in the lake and other similar lakes with high WLFs.

The effects of restored hydrologic connectivity on floodplain trapping vs. release of phosphorus, nitrogen, and sediment along the Pocomoke River, Maryland USA

River channelization and artificial levees have decreased the hydrologic connectivity of river-floodplain systems around the world. In response, restoration through enhancing connectivity has been advocated to improve the functions of floodplains, but uncertain benefits and the possibility of phosphate release from re-flooded soils has limited implementation. In this study, we measured change in floodplain P, N, and sediment mass balances after restoration along channelized reaches in the lowland Pocomoke River, Maryland USA. Two floodplains (one headwater, one mainstem) restored through partial levee breaches were compared to two additional mainstem floodplains (one natural unchannelized, one unrestored channelized). Potential soluble reactive P (SRP) release from soil cores during experimental laboratory floods; soil P, Fe, and Al fractionation; and deposition and P and N content of sediment were measured before and after the restoration period, as well as in situ inputs and release of SRP and dissolved inorganic N from soils after restorations. Potential SRP release, during both the before and after restoration period, was greatest at the channelized mainstem and restored mainstem sites, lower at the restored headwater site, and small at the natural mainstem site. Both restored sites had smaller potential SRP release after restoration compared to before restoration. In situ SRP release slightly exceeded inputs to soils at connected sites during the post-restoration period, with less net release at the restored sites compared to the natural mainstem site. The magnitude of gross and net SRP release from soils in the field was smaller than, and uncorrelated with, potential SRP release estimated from laboratory experimental floods. Gross soil SRP release rates in the field were predictable using the ratio of soil oxalate-extractable P/Al. Sedimentation inputs of P and N increased at all sites during the post-restoration period, with rates at restored sites intermediate compared to the much higher rates at the natural mainstem site and somewhat lower rates at the channelized mainstem site. These sediment inputs of nutrients were much larger than rates of inorganic P and N release from soils, indicating net trapping of P and N after restoration. Restoring floodplain hydrologic connectivity showed moderate success at increasing the trapping of P, N, and sediment, with relatively little phosphate release, and therefore improving water quality.

Effects and Differences of the Release of Dissolved Organic and Inorganic Phosphorus in Different Sediments Covered by Different Materials of Erhai Lake

In this work, the effects of four covering materials on the release of total dissolved phosphorus (DTP), dissolved organic phosphorus (DOP), and soluble reactive P (SRP) in different sediments of Erhai Lake were simulated. The results showed that the max release of DTP was reduced in covering material, which attributed to the changes of pH, Eh and characteristics of dissolved organic matter (DOM) by the effect of covering material. The application of iron oxide material significant reduced the release of DTP in the northern and southern part of the lake, with decrease rate of 44.3% and 35.7%, respectively. by contrast, the application of aluminum oxide material significant reduced the release of DTP in the middle part sediment, with decrease rate of 29.6%. Furthermore, the release of SRP and DOP in different sediments has significant difference after added different material. In northern part of sediment, the release of SRP and DOP reduced by 35.6% and 36.2% after added iron oxide material. This is because iron oxide can reduce the pH and Eh but increase the availability of DOM in northern, and then benefits for inhibiting the release of SRP and DOP. In the middle, the release of sediment SRP and DOP reduced by 28.9% and 31.6% after added aluminum oxide material. This is because the aluminum oxide can facilitate the availability of DOM in middle, and then inhibits the release of SRP and DOP. In southern part of the lake, the release of sediment SRP and DOP reduced by 47.4% and 16.5% after added iron oxide material. This is largely attributed to the effect of iron oxide on the pH and Eh. Therefore, to control the release of P in the sediment from Lake Erhai, iron oxide material should be selected in the northern and southern parts, whereas aluminum oxide should be selected in the middle part of the lake.

Algal Demand Drives Sediment Phosphorus Release in a Shallow Eutrophic Cove

Abstract. Algae play an important role in the internal nutrient cycling of shallow lakes and coves. Algae of shallow water bodies have been shown to thrive and even lead to eutrophic conditions despite a lack of measurable quantities of biologically available phosphorus (P) in the water during summer months. To study how sediment P release and algal growth are connected, water and sediment samples were collected in a shallow eutrophic cove on Beaver Lake in northwest Arkansas. Water quality profiles depicting temperature, dissolved oxygen, nutrients, metals, and photic zone chlorophyll-a were collected weekly from 21 May to 10 July 2018 at three points in the cove: one shallow, one at the cove midpoint, and one at the deepest part of the cove. Cove sediment samples were collected at similar points as the water quality samples for equilibrium P concentration (EPCo) analysis, sediment core incubation, and sediment composition. EPCo for the sediments ranged from 0.024 to 0.027 mg L-1. Sediment cores exposed to aerobic conditions typical of shallow areas had P release rates ranging from 1.37 to 2.02 mg m-2 d-1. Concentrations of soluble reactive P (SRP) in the water column from the weekly water quality sampling averaged 0.002 ±0.003 mg L-1, and photic zone SRP concentrations averaged 0.002 ±0.004 mg L-1 for all sampling sites. The chlorophyll-a concentration increased from 10 to 40 µg L-1 during the period from 21 May to 25 June. When SRP &amp;lt;&amp;lt; EPCo, conditions favor the release of SRP from sediments to the overlying water. This was confirmed with the aerobic sediment core incubation in which algal demand was controlled using dark conditions and the release rates were &amp;gt;1.37 mg L-1 d-1. Core aerobic release rates and EPCo conditions both confirmed the release of P under aerobic conditions; however, it appears that algal demand sustained low SRP conditions. This created a nutrient cycle in which algae imposed a nutrient gradient favoring P release by keeping SRP conditions below the EPCo. This study indicates that algal growth potential in shallow water bodies is not limited by SRP concentrations measured within the water column. Studies of shallow water bodies with low SRP concentrations and high productivity should look to the sediments as a source of P to fuel algal growth. Finally, these findings suggest that coves play an integral part in algal production and should not be overlooked when determining the overall P budget for a lake or reservoir. Keywords: Aerobic phosphorus release, Equilibrium phosphorus concentration, Sediment core incubation.

Phosphorus Mobilization in Flooded Riparian Soils From the Lake Champlain Basin, VT, USA

Riparian soils and sediments have the potential to release bioavailable phosphorus, contributing to water quality degradation. Here, we measured phosphorus (P) release to soil porewater (PW) and overlying floodwater (FW) in 12 riparian buffer and 2 agricultural floodplain soils from northwestern Vermont, USA to evaluate P mobilization risk and determine relationships with soil properties (total P, labile P concentrations, pH, organic matter). Duplicate samples (field-moist) were flooded with distilled water in polyethylene beakers modified for PW sampling. Soluble reactive P (SRP) (PW and FW) and PW ferrous iron (Fe2+) concentrations were measured over a 75-day period in the laboratory. Soluble unreactive P (SUP) in PW was also measured twice. Two samples were also flooded after air-drying soil to determine the influence on SRP release. Results showed that PW-SRP tended to increase over time, whereas FW-SRP tended to decrease. The ratio of PW-SRP on day-75 to initial concentrations ranged from 0.21 to 8.4 (mean = 3.2 ± 2.7), while the ratio for FW-SRP was 0.19 to 1.3 (mean = 0.63 ± 0.39). Mean PW- and FW-SRP ranged from 0.03 to 2.2 mg/L and 0.01 to 0.33 mg/L, respectively. Biochemical reduction occurred in 13/14 soils as indicated by PW-Fe2+, while FW remained oxidized (mean dissolved oxygen on day 75 = 6.8 ± 0.3 mg/L). Soil pH was positively related to mean PW- (R2 = 0.48, P = 0.006) and FW-SRP (R2 = 0.47, P = 0.007), whereas mean PW-SUP was inversely related to pH (R2 = 0.44, P = 0.01). Mean ratio of PW-SRP:FW-SRP was 3.5 ± 1.9 and increased with soil pH (R2 = 0.59, P = 0.001). Modified Morgan extractable P was the best predictor of FW and PW-SRP release. Flooding dry soil decreased FW dissolved oxygen concentrations while increasing PW-Fe2+, PW-SRP, and SRP mobilization to FW relative to a field-moist state. Results indicate that SRP release could pose water quality concerns, however mobilization to overlying water was limited by re-adsorption of released P. Our results highlight the importance of integrating measures of labile soil P with hydrologic flow pathways in models to better predict P transport in riparian landscapes.

Non-domestic phosphorus release in rivers during low-flow: Mechanisms and implications for sources identification

A common assumption in phosphorus (P) load apportionment studies is that P loads in rivers consist of flow independent point source emissions (mainly from domestic and industrial origins) and flow dependent diffuse source emissions (mainly from agricultural origin). Hence, rivers dominated by point sources will exhibit highest P concentration during low-flow, when flow dilution capacity is minimal, whereas rivers dominated by diffuse sources will exhibit highest P concentration during high-flow, when land-to-river hydrological connectivity is maximal. Here, we show that Soluble Reactive P (SRP) concentrations in three forested catchments free of point sources exhibited seasonal maxima during the summer low-flow period, i.e. a pattern expected in point source dominated areas. A load apportionment model (LAM) is used to show how point sources contribution may have been overestimated in previous studies, because of a biogeochemical process mimicking a point source signal. Almost twenty-two years (March 1995–September 2016) of monthly monitoring data of SRP, dissolved iron (Fe) and nitrate-N (NO3) were used to investigate the underlying mechanisms: SRP and Fe exhibited similar seasonal patterns and opposite to that of NO3. We hypothesise that Fe oxyhydroxide reductive dissolution might be the cause of SRP release during the summer period, and that NO3 might act as a redox buffer, controlling the seasonality of SRP release. We conclude that LAMs may overestimate the contribution of P point sources, especially during the summer low-flow period, when eutrophication risk is maximal.

Sustainable management of biosolid phosphorus: a field study

AbstractStabilized wastewater biosolids are a renewable resource for improving soil and crop quality, but their regular application can rapidly elevate soil available phosphorus (P) (e.g. Olsen‐P[OP]) leading to increased transfer of soluble reactive P (SRP) in land run‐off causing eutrophication. To assess the eutrophication risk of biosolid P recycling, 143 arable fields with different biosolid P input histories, and representing different soil type and biosolid type combinations, were sampled and their P chemistry determined. Differences in soil total P between the surveyed fields were used as the best measure of net biosolid P inputs. Rates of soil OP increase (range 3–11% of soil total P, mean 7%) were lowest on a P‐fixing soil and tended to increase more on sandy soils (6–9%) and on loamy soils receiving biosolids dosed with both iron (Fe) and lime (9–11%). Potential release of SRP to run‐off was measured as water‐extractable P (WEP) and varied widely (6–52% of soil OP). WEP concentrations were lowest on clayey soils, and where biosolids containing P‐binding elements [calcium (Ca) or Fe, but not together] were applied. The relationship between OP and WEP was therefore highly dependent on both soil type and biosolid type. However, analysis of soil P sorption parameters indicated that eutrophication risk on loamy and clayey soils was significantly reduced when OP represented &lt;20% of the soil P sorption capacity. Our results suggest that biosolids could be more sustainably managed by matching biosolid type to soil type and P fertility status.

Are Floodplain Soils a Potential Phosphorus Source When Inundated That Can Be Effectively Managed?

Core Ideas Dissolved phosphorus is released from floodplain soils when inundated. Phosphorus release rates are positively correlated with soil test and water‐extractable P in soil. Water treatment residuals decrease P release rates, providing a potential mitigation option. The growing concern over phosphorus (P) and water quality has led to questions as to where the loads originate and how to control landscape inputs from the watershed. We collected soil cores from two locations in the Illinois River watershed to examine the relationship between stored soil P and the amount of soluble reactive P (SRP) released into the water when soils are flooded. After inundation, P flux calculations for durations of ∼24 h ranged from less than 0.1 to 9.3 mg SRP m−2 h−1. Soil test P (STP), measured as water‐extractable P and Mehlich‐III P, correlated with SRP flux, where higher STP resulted in increased P flux to the overlying water. Floodplain soils have the potential to be a P source, potentially releasing more than 1600 mg m−2 yr−1 (&gt;16 kg ha−1 yr−1) depending on length and frequency of inundation and on STP content. Applying water treatment residuals (WTRs) significantly reduced P flux from the cores. Hence, WTR application to critical source areas provides a mitigation strategy to manage floodplain soils and potential SRP release.

Effects of organic matter and submerged macrophytes on variations of alkaline phosphatase activity and phosphorus fractions in lake sediment

Organic matter and submerged plants may affect internal phosphate loading in lake sediment. In this study, we investigated the changes of alkaline phosphatase activity (APA) and phosphorus (P) fractions in lake sediment by adding organic matter (0.0%, 0.5% and 1.0% of dry weight) and plant submerged plants under experimental conditions. Results indicated that the APA in sediments significant increased after 50 days incubation than at 7 days. The APA in the treatments by adding organic matter and submerged plants increased by 26.37%–61.78% than that of control after 7 days incubation, and increased by 1.00%–29.51% at 50 days, indicating both organic matter and submerged plants may remarkable affect APA in sediment, especially for the early stage of incubation. In addition, the soluble reactive P (SRP) concentrations of the overlying water increased significantly with increasing sediment organic matter, possibly related to increase of APA in sediment. However, the release of SRP was obvious restrained due to absorption of submerged plant. TP and P fraction in sediment decreased with increasing incubation time, but the decrease of TP content in sediment was mainly from NaOH–P and OP sources, but not from HCl–P and IP. Effects of organic matter and submerged plants on P fractions in sediment mainly occurred in NaOH–P and OP fractions. At the end of experiments, the contents of NaOH–P and OP in the treatments by adding organic matter and submerged plant decreased by 5.46%–20.47% and 7.87%–21.46%, respectively. These results indicated that the relative importance of organic matter and submerged plants during the release and transformation of P in lake sediment.

Sediment phosphorus flux in an Oklahoma reservoir suggests reconsideration of watershed management planning

A reservoir model of Lake Wister, Oklahoma, indicated that internal sources dominated phosphorus (P) loading to the waterbody, and that a watershed management plan need not address external P sources. To test this claim, we evaluated internal P loading by measuring sediment oxygen demand (SOD) and quantifying soluble reactive P (SRP) release from sediments to the overlying water column. Sediment cores from 3 sites were incubated at 21 C under quiescent conditions. Average SOD rates were between 9.9 and 22.6 mg/m2/h (240–540 mg/m2/d) across the three sites, where the shallow headwaters site had the least SOD. Average SRP release rate measurements varied from <0 to 3.30 mg/m2/d across the sites, and measurements were greatest under anaerobic conditions in the cores collected from deep water near the dam and the water intake structure. Measured values were an order of magnitude less than those used to calibrate the previous reservoir model. The new data contradict the findings of the earlier reservoir model and suggest that internal P cycling would not be the dominant P source. Thus, external P sources to Lake Wister must be considered in watershed management planning. A watershed-based strategy that focuses on both internal and external P sources is needed to improve overall water quality in this drinking water supply reservoir.

Internal loading of phosphorus in a sedimentation pond of a treatment wetland: Effect of a phytoplankton crash

Sedimentation ponds are widely believed to act as a primary removal process for phosphorus (P) in nutrient treatment wetlands. High frequency in-situ P, ammonium (NH 4 +) and dissolved oxygen measurements, alongside occasional water quality measurements, assessed changes in nutrient concentrations and productivity in the sedimentation pond of a treatment wetland between March and June. Diffusive equilibrium in thin films (DET) probes were used to measure in-situ nutrient and chemistry pore-water profiles. Diffusive fluxes across the sediment–water interface were calculated from the pore-water profiles, and dissolved oxygen was used to calculate rates of primary productivity and respiration. The sedimentation pond was a net sink for total P (TP), soluble reactive P (SRP) and NH 4 + in March, but became subject to a net internal loading of TP, SRP and NH 4 + in May, with SRP concentrations increasing by up to 41 μM (1300 μl − 1 ). Reductions in chlorophyll a and dissolved oxygen concentrations also occurred at this time. The sediment changed from a small net sink of SRP in March (average diffusive flux: − 8.2 μmol m − 2 day − 1 ) to a net source of SRP in June (average diffusive flux: + 1324 μmol m − 2 day − 1 ). A diurnal pattern in water column P concentrations, with maxima in the early hours of the morning, and minima in the afternoon, occurred during May. The diurnal pattern and release of SRP from the sediment were attributed to microbial degradation of diatom biomass, causing reduction of the dissolved oxygen concentration and leading to redox-dependent release of P from the sediment. In June, 2.7 mol-P day − 1 were removed by photosynthesis and 23 mol-P day − 1 were supplied by respiration in the lake volume. SRP was also released through microbial respiration within the water column, including the decomposition of algal matter. It is imperative that consideration to internal recycling is given when maintaining sedimentation ponds, and before the installation of new ponds designed to treat nutrient waste.

Periphyton as a potential phosphorus sink in the Everglades Nutrient Removal Project

Phosphorus uptake and release by periphyton mats were quantified in the Everglades Nutrient Removal Project (ENRP) to evaluate the potential for periphyton P removal. Short-term P uptake rates were determined by incubating cyanobacteria ( Oscillatoria princeps and Shizothrix calcicola) and Chlorophycean (primarily Rhizoclonium spp.) algal mat samples for 0.5–2 h under ambient conditions in BOD bottles spiked with soluble reactive P (SRP). Cyanobacterial mats removed P more than twice as fast (80–164 μg P h −1 g −1 AFDM) as Chlorophycean mats (33–61 μg P h −1 g −1 AFDM) during these incubations. In a longer term study, fiberglass cylinders were used to enclose 1.8 m 2 plots within the wetland and were dosed weekly for 7 weeks with: (1) no nutrients; (2) SRP (0.25 g P m −2 week −1); or (3) SRP plus nitrate (0.42 g N m −2 week −1) and ammonium (0.83 g N m −2 week −1). Phosphorus uptake rates by this periphyton assemblage, which was dominated by the chlorophytes Stigeoclonium spp. and Oedogonium spp., were measured weekly and were similar among nutrient treatments on most dates, indicating that the algal storage compartment for P was not saturated despite repeated P additions. Decomposition rates and P loss by cyanobacteria and Chlorophycean mats were determined by measuring biomass loss and SRP release in darkened BOD bottles over 28–42 day periods under anaerobic and aerobic conditions. First-order aerobic and anaerobic decomposition rates for cyanobacterial mats ( k = 0.1095 and 0.1408 day −1, respectively) were 4–20-fold higher than rates for Chlorophycean mats ( k = 0.0066 and 0.0250 day −1, respectively) and cyanobacteria released considerably more P back to the water column. Our findings suggest that periphyton can be an important short-term sink for P in treatment wetlands and that retention is strongly affected by the taxonomic composition of the periphyton assemblage.

Influence of beaver ponds on the phosphorus concentration of stream water

A study of five beaver ponds in central New York State showed that the ponds differed in how they influenced streamwater P concentration. Processes in three of the ponds increased soluble reactive P (SRP) of the stream water during warmer months, and also dramatically increased SRP in one of these ponds (Black Warrior) during an extended period of ice cover. The remaining two ponds were consistent in reducing SRP in stream water at all times of the year. Total soluble P trends essentially followed those of SRP at each of the ponds, while total P differed from SRP at four of the sites. Microbial respiration created anaerobic conditions within the pond sediments which influenced biogeochemical cycling of P. Anaerobic conditions and H2S production occurred at Black Warrior pond during the extended winter ice cover, resulting in SRP release. My results showed that elevated levels of P may occur for only short distances downstream of ponds before equilibrium processes reduce the concentration.

Contribution of bacteria to release and fixation of phosphorus in lake sediments

Cycling of phosphorus at the sediment‐water interface is traditionally considered to be controlled by pH‐ and redox‐dependent, abiotic processes, such as formation and dissolution of FeOOH‐PO4 complexes. In this study, however, a large part of total P in sediments of Lake Sempach, an 87‐m deep eutrophic lake, was estimated to be incorporated in bacterial biomass. Laboratory experiments indicated that sediment microorganisms can rapidly take up and release soluble reactive P (SRP), depending on redox conditions, and that sterilization of oxic sediments decreased their SRP sorption capacity. In an in situ experiment conducted in the lake, bacteria also contributed considerably to SRP fixation when water enclosed within a sediment flux chamber was reoxygenated following anoxia. Moreover, in that experiment and in data sets from several other lakes, anoxic releases of Fe and P from sediments appeared to be partly uncoupled. As part of an ongoing revision of the classical model for P exchange across the sediment‐water interface, these results provide direct evidence that fixation and release of SRP may be controlled partly by redox‐dependent changes in microbial physiology, as well as by production and decomposition of microbial biomass.