Soluble Reactive Phosphate Concentrations Research Articles

Phosphorus starvation response genes and function coupling: A mechanism to regulate phosphorus availability in a subtropical estuary

Phosphorus (P) plays an important role in regulating primary production in estuarine environments. However, knowledge of the P-functional gene composition of microbial communities and the mechanisms of microbial adaptation to changes in available P in estuaries remain limited. This study coupling 16 s rDNA and metagenomics sequencing was conducted to reveal the relationship between P cycling functional genes, microbial interactions, and P availability in the Jiulong River Estuary. The results showed that the relative abundance of P cycling functions genes was highest in winter, and lowest in summer. Spatially, the total relative abundance of P cycling functions genes was higher in the riverward than that in the seaward. P cycling functional microbial interactions and P cycling gene coupling were strongest in summer and in the seaward. Changes in both temperature and salinity had significant direct and indirect effects on P cycling function, and the influence of salinity on P cycling function was greater than that on the microbial community in the estuary. Salinity had significant direct negative effects on inorganic P-solubilization (IP), organic P-mineralization (OP), and P uptake and transport functions (PT). Whereas, salinity had a significant positive effect on P-starvation response regulation (PR) function. Thus, salinity and microbial communities regulate the soluble reactive phosphate concentrations in estuarine environments by strengthening internal coupling among P cycling functions, promoting PR function, and facilitating PT gene expression. PR is the most important predictors, PR, PT, and PR-PT together explained 38.56 % of the overall soluble reactive phosphorus (SRP) variation. Over 66 % of the explained SRP variations can be predicted by the PR, PT, and PR-PT functional genes. This finding improves the knowledge base of the microbial processes for P cycling and provides a foundation for eutrophication management strategies in the estuary.

Introducing La(OH)3 nanoparticles into attapulgite for the control of sediments internal phosphorus release: Effectiveness, mechanisms, and microbial community response

In-situ passivation of engineering materials is an economical and effective method to control internal phosphorus load in aquatic systems. However, few studies have simulated aerobic and anaerobic environments to compare the engineering materials control sediment phosphorus release performance with or without sediment re-suspension. In this study, we prepared and optimized lanthanum modified thermally attapulgite (LMTA) for sediment phosphorus immobilization with a maximum adsorption capacity of 97.99 mg/g. An 88-day sediment core cultivation experiment revealed that LMTA reduced the concentration of soluble reactive phosphate (SRP) and total phosphorus (TP) by 89.3% and 79.4% in absence of re-suspension, and by 89.8% and 78.3% with re-suspension, respectively. LMTA also transformed sediment Mobile-P into HCl-P and Res-P, which are inert phosphorus forms. Moreover, high-throughput sequencing showed that Nitrospirae abundance was significantly increased with LMTA, which could promote the water nitrogen cycle. The results confirmed that LMTA effectively controls internal phosphorus release, even under sediment re-suspension conditions.

Effects of Weather Extremes on the Nutrient Dynamics of a Shallow Eutrophic Lake as Observed during a Three-Year Monitoring Study

The formation of algal and cyanobacterial blooms caused by the eutrophication of water bodies is a growing global concern. To examine the impact of extreme weather events on blooms, eutrophication-related parameters (e.g., water temperature, nitrate, ammonium, nitrite, and soluble reactive phosphate (SRP)) were quantitatively assessed monthly over three years (2017–2019) at Lake Seeburg (Central Germany), a shallow eutrophic lake with regular cyanobacterial blooms. In addition, SRP concentrations in sediment pore water were assessed monthly for one year (2018). The monitoring period included a three-day extremely heavy rain event in 2017 as well as a severe drought in summer 2018. No such extreme weather conditions occurred in 2019. After the heavy rain event in 2017, anoxic water containing high levels of ammonium and SRP entered the lake from flooded upstream wetlands. This external nutrient spike resulted in a heavy but short (3 weeks) and monospecific cyanobacterial bloom. A different situation occurred during the exceptionally hot and dry summer of 2018. Especially favored by high water temperatures, SRP concentrations in sediment pore waters gradually increased to extreme levels (34.4 mg/L). This resulted in a strong and sustained internal SRP delivery into the water column (69 mg/m2·d−1), which supported the longest-lasting cyanobacterial bloom (3 months) within the three-year monitoring period. Subsequent biomass decay led to oxygen-depleted conditions in the bottom waters, elevated ammonium, and, later, nitrate concentrations. Our observations demonstrate the particular effects of extreme weather events on nutrient dynamics and the phytoplankton composition in the lake. As the frequency and intensity of such events will likely increase due to climate change, their impacts need to be increasingly considered, e.g., in future remediation strategies.

Water soluble reactive phosphate (SRP) in atmospheric particles over East Mediterranean: The importance of dust and biomass burning events

The importance of dust and biomass burning episodes on the atmospheric concentration of water-soluble reactive phosphate (SRP) was determined in the eastern Mediterranean. SRP was measured with a new rapid real-time automated analytical system with a time resolution of a few minutes per sample and with an extremely low detection limit. The average atmospheric concentration of SRP during the sampling campaign was estimated at 0.35 ± 0.25 (median 0.30) nmol P m−3. The maximum concentration of SRP (3.08 nmol P m−3) was recorded during an intense dust episode, and was almost ten times higher than the campaign average, confirming that Saharan dust was an important primary source of bioavailable P to the eastern Mediterranean, especially during the spring period when 60% of the events occurred. Predicted increases in the frequency and intensity of dust storms in the area will enhance the role of the atmosphere as a source of bioavailable P for the Mediterranean marine ecosystem. During the warm period, when Northerly winds prevailed, biomass burning processes contributed significantly to soluble phosphorus delivered from atmospheric sources to the eastern Mediterranean. These inputs during warm periods are especially important for the Eastern Mediterranean, where biological productivity is strongly limited by nutrient availability.

Effect of <i>Pomacea canaliculata</i> grazing on three submerged macrophytes and the related physicochemical factors

外来种福寿螺（Pomacea canaliculata）相较我国本土螺类其牧食量更大且繁殖速度更快，对栖息地水生植物的现存量和实施水生植被恢复的生态治理工程的成功性可能构成威胁，目前对福寿螺影响浅水湖泊沉水植物的重建缺乏足够的研究.本文通过设置不同沉水植物种类组合系统，研究福寿螺对3种常用于浅水富营养化湖泊治理的沉水植物密刺苦草（Vallisneria denseserrulata）、轮叶黑藻（Hydrilla verticillata）、穗花狐尾藻（Myriophyllum spicatum）的牧食偏好以及不同植物配置系统理化因子的响应变化，结果表明福寿螺对沉水植物植株附着偏好为密刺苦草>轮叶黑藻>穗花狐尾藻，而牧食破坏强度为轮叶黑藻>穗花狐尾藻>密刺苦草，轮叶黑藻最容易受到福寿螺牧食影响而快速消亡，穗花狐尾藻叶片也会被全部牧食仅剩下茎，而苦草存活受到的影响较小.福寿螺会导致轮叶黑藻+密刺苦草组合系统中总氮、氨氮、总磷、正磷酸盐浓度显著升高，而密刺苦草+穗花狐尾藻组合中总磷、正磷酸盐浓度显著升高，但是在轮叶黑藻+穗花狐尾藻组合中仅总氮浓度显著升高.研究表明福寿螺能够影响沉水植物间的竞争关系，但是3种沉水植物均不能阻止福寿螺的牧食；福寿螺牧食会显著降低沉水植物生物量，最终会影响草型清水态系统的稳定性.;Compared with native snails in China, Pomacea canaliculata snails exert a higher grazing pressure on plants and have faster growth and reproduction rates, which may negatively affect aquatic plants' standing stock and ecological reestablishment. However, few studies have examined the potential effects of the presence of P. canaliculata on submerged macrophyte reestablishment. In this study, we assessed the preference of P. canaliculata for three submerged plants, namely Vallisneria denseserrulata, Hydrilla verticillata, and Myriophyllum spicatum—which have been largely planted for recovering Chinese eutrophic shallow lakes. The results indicated that the attachment preference of P. canaliculata for submerged macrophytes was in the following order: V. denseserrulata>H. verticillata>M. spicatum. Moreover, P. canaliculata grazing negatively affected plant survival in the following order of magnitude: H. verticillata>M. spicatum>V. denseserrulata. H. verticillata was the most vulnerable to snail grazing and died out rapidly. M. spicatum leaves had been completely consumed by the end of the experiment. V. denseserrulata was the least influenced by P. canaliculata. Compared with the controls, the concentrations of total nitrogen (TN), ammonia nitrogen (NH₃-N), total phosphorus (TP), and soluble reactive phosphate (SRP) were higher with the H. verticillata + V. denseserrulata treatment; TP and SRP concentrations were higher with the V. denseserrulata + M. spicatum treatment; and TN concentrations were higher with the V. denseserrulata + M. spicatum treatment. These results suggest that the grazing preference of P. canaliculata alters the competitive advantage of submerged macrophyte. However, none of the submerged macrophytes prevented P. canaliculata grazing, resulting in decreases in the production of the submerged macrophytes and in the likelihood of clear-water state establishment.

Distribution Characteristics and Spatial Differences of Phosphorus in the Main Stream of the Urban River Stretches of the Middle and Lower Reaches of the Yangtze River

Excessive phosphorus is the main problem of water pollution in the main stream of the Yangtze River, while it is not clear about the distribution characteristics and spatial differences of phosphorus in the urban river stretches of the middle and lower reaches of the Yangtze River. In this study, a field survey in June 2014 revealed that the average particulate phosphorus (PP) concentration ranged from 0.195 mg/L to 0.105 mg/L from Wuhan (WH) in the middle reaches of the Yangtze River to Shanghai (SH, 1081 km from WH) in the lower reaches of the Yangtze River, and the average PP-to-the total phosphorus (TP) ratio decreased from 85.71% in WH to 45.65% in SH, while the average soluble reactive phosphate (SRP) concentration ranged from 0.033 to 0.125 mg/L, and the average SRP-to-total dissolved phosphorus (TDP) ratio increased from 60.73% in WH to 88.28% in SH. In general, PP was still an important form of TP in the middle and lower reaches of the Yangtze River. The concentrations of PP and SRP at different sampling locations and water depths in the same monitoring section showed differences, which might be related to the transportation and sedimentation of suspended sediment (SS) and differences in the location of urban sewage outlets. Historical data showed that the concentration and particle size of the SS decreased over time, while the discharge of wastewater also increased over time in the Yangtze River Basin. The measured results showed that there was a significant positive correlation between SS and PP. As a result, the concentration of SRP might increase in the middle and lower reaches of the Yangtze River. If the SRP concentration is not properly controlled, the degree of eutrophication of water body could significantly increase in the Yangtze River estuary, the riparian zone of the urban river stretches, the tributary slow-flow section, and the corresponding lakes connected with the Yangtze River.

Study on Characteristics of Nitrogen and Phosphorus Loss under an Improved Subsurface Drainage

Agricultural drainage plays an effective role in preventing waterlogging and salinity disasters and also is the main transport pathway for agricultural non-point source pollutants into rivers and lakes. Hence, the water quality of agricultural drainage should be a point of focus. In this paper, nitrogen and phosphorus loss under improved subsurface drainage with different filter materials (gravel, layered sand-gravel, mixed sand-gravel, straw) were studied by a three-year field experiment (2016–2018) compared with the conventional subsurface drainage. The pH values, total nitrogen, ammonia nitrogen, nitrate nitrogen, total phosphorus and soluble reactive phosphate were considered. The results showed that the nitrogen and phosphorus concentrations of drain outflow under improved subsurface drainage with gravel filter were larger than that with layered sand-gravel filter and mixed sand-gravel filter. The improved subsurface drainages with layered sand-gravel filter and mixed sand-gravel filter had an effect on reducing the ammonia nitrogen, total phosphorus and soluble reactive phosphate concentrations of the outflow. Meanwhile, the characteristics of nitrogen and phosphorus loss under the improved subsurface drainage with straw filter were different from that with layered sand-gravel filter and mixed sand-gravel filter. For the improved subsurface drainage with layered sand-gravel filter outflow, the ammonia nitrogen, total phosphorus, and soluble reactive phosphate concentrations were about 13%–78%, 38%–63%, 40%–68% less, and total nitrogen, nitrate nitrogen concentrations were 24%–80%,18%–96% more than that under conventional subsurface drainage. Meanwhile, for the improved subsurface drainage with straw filter outflow, compared with conventional subsurface drainage outflow, the percentage changes of the total nitrogen, nitrate nitrogen, ammonia nitrogen, total phosphorus and the soluble reactive phosphate concentrations were about −76%–62%, −77%–78%, −152%–−274%, −103%–−400% and −221%–−291%, respectively. Additionally, in the outflow of all subsurface drainage patterns, there were much higher total nitrogen and nitrate nitrogen concentrations which should be focused on and the agricultural water management should be adopted.

Nutrient release from sediments and biological nitrogen fixation: Advancing our understanding of eutrophication sources in Lake Victoria, Tanzania

AbstractIntensification of anthropogenic activities in the three riparian countries bordering the shoreline of Lake Victoria is exacerbating eutrophication in the main body of the lake. The present study evaluated the importance of sediments and biological nitrogen fixation as sources of nutrient enrichment into Lake Victoria in Magu, Mwanza and Kayenze bays influenced by different anthropogenic activities, over a period of 7 months. Kayenze Bay is a relatively pristine site, while higher anthropogenic activities occur in the Magu Bay and Mwanza North Bay areas. Sediment cores were retrieved from each sampling site and transported to the laboratory for nutrient concentrations and flux analyses. In situ nitrogen fixation rates also were measured in the water column. The results indicated the sediment–water interface in Magu Bay exhibited significantly higher concentrations of nitrate‐N and a net release of nitrate‐N, compared to Mwanza North Bay and Kayenze Bay (p < 0.001). The sediment–water interface in Magu Bay also exhibited a significant net release of total phosphate towards the water column, compared to Mwanza Bay (p < 0.001). The sediment–water interface in Mwanza North Bay exhibited higher ammonium‐N concentrations, and net release of ammonium‐N and total nitrogen than did Magu and Kayenze Bays (p < 0.001). The sediment–water interface in Mwanza and Magu Bays exhibited higher total nitrogen and soluble reactive phosphate concentrations than Kayenze Bay (p < 0.001). Their sediments also released net fluxes of soluble reactive phosphate to the water column than did Kayenze Bay (p < 0.001). In contrast, the Kayenze Bay sediments acted as a sink of ammonium‐N from the water column, compared to Mwanza North and Magu Bays (p < 0.001). Biological nitrogen fixation rates were significantly higher during the rainy season than the dry season (p < 0.05), although no spatial variations in biological nitrogen fixation existed among the three sites (p > 0.05). The present study indicated the water column and sediments in Magu Bay and Mwanza North Bay, characterized by high anthropogenic activities are rich in nitrate‐N, ammonium‐N, total nitrogen and soluble reactive phosphate, compared to the relative pristine Kayenze Bay. Anthropogenic activities and sediments may well be important sources of nutrients enrichment to the overlaying waters, thereby enhancing eutrophication of Lake Victoria. Management strategies are required to reduce external releases and internal nutrient fluxes to enhance the lake ecosystem health.

Niche-breadth of freshwater macrophytes occurring in tropical southern African rivers predicts species global latitudinal range

The study tested the hypothesis that measurement, using multivariate Principal Components Analysis (PCA), of the niche-breadth of river macrophyte species in southern tropical Africa, may predict their larger-scale biogeographical range. Two measures of niche-breadth were calculated for 44 riverine macrophyte species, from 20 families commonly occurring in Zambia, using an approach based on PCA ordination with 16 bio-physico-chemical input variables. These included altitude, stream order, stream flow, pH, conductivity and soluble reactive phosphate concentration (SRP). In the absence of additional chemical water quality data for Zambian rivers, invertebrate-based measures of general water quality were also used. These were benthic macroinvertebrate Average Score per Taxon (ASPT), and individual abundance of nine macroinvertebrate families with differing water quality tolerance, indicated by their Sensitivity Weightings within the Zambian Invertebrate Scoring System (ZISS). Macrophyte large-scale latitudinal range was derived from world geopositional records held by online databases, and additional records held by the authors. The two niche-breadth metrics divided the species into narrow-niche and intermediate/broad-niche categories, showing significant variation (from one or both of correlation and ANOVA test outcomes) in altitude, stream flow, conductivity, SRP, pH and ASPT, but not stream order. Macrophyte alpha-diversity (as a measure of number of individual niches co-existing per habitat) showed no significant relationship with individual species niche-breadth. Narrow-niche species included a higher proportion of Afrotropical endemics than did species with broader niche size. There were significant predictive relationships between macrophyte niche-breadth and latitudinal range of the target species at global and Afrotropical scales, but not for the Neotropics.

Surface water quality monitoring of an agricultural watershed for nonpoint source pollution control

Water pollution is a major environmental problem in the United States. To improve the surface water quality of the 2,493 ha (6,160 ac) Coulee Baton watershed in Louisiana, a collaborative nonpoint source pollution control study was initiated in 2004. Conservation measures and best management practices (BMPs) including cross-fencing of pasturelands (726.9 m [2,385 ft]), irrigation land leveling (12.9 ha [32 ac]), grade stabilization structures (two), irrigation water pipeline (975.4 m [3,200 ft]), and a livestock well covering a total of 92.7 ha (229 ac) of agricultural land, and repair or replacement of 80 septic systems in the watershed were voluntarily implemented by landowners and homeowners. Water samples were collected from seven monitoring sites for 66 rain events from September 24, 2009, to August 9, 2011. Laboratory determinations of water samples included total suspended solids (TSS), total dissolved solids (TDS), total solids (TS), five-day biological oxygen demand (BOD5), nitrate/nitrite-nitrogen (NO3/NO2-N), soluble reactive phosphate (SRP), total phosphorus (TP), total Kjeldahl N (TKN), chloride (Cl), fluoride (Fl), sulfate (SO4), and fecal coliform counts. Surface water temperature, dissolved oxygen (DO), turbidity, conductivity, and pH were determined in the field using YSI Sonde (YSI Incorporated, Yellow Springs, Ohio). For the watershed, DO, BOD5, and TS concentrations and fecal coliform count ranged, respectively, between 1.2 and 14.1 mg L−1 (ppm), 2 and 40.1 mg L−1, 35 and 5,719 mg L−1, and 400 × 106 and 17 × 106 most probable number (MPN) per 100 mL. The months of March, April, June, and September showed, on average, higher concentrations of TS and TDS, fecal coliform count, NO3/NO2-N, and SRP and TP, respectively. As compared to the ongoing BMPs, the post-BMPs, TSS, NO3/NO2-N, SRP, and BOD5 concentrations, on average, were lower by 56.2%, 23.1%, 82.5%, and 27.4%, respectively. Developed land use types and the failed septic systems were identified as major sources of fecal coliform pollution. These results suggest comprehensive strategies are necessary for effective nonpoint source pollution control in agricultural watersheds.

Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications

In California’s water-seeded rice systems, algal/cyanobacterial biomass can be a problem during rice establishment and can lead to yield reductions. Laboratory, enclosure, and field-scale experiments were established to evaluate the effects of fertilizer P management on algal/cyanobacterial growth. Two field-scale experiments evaluated the response of algal/cyanobacterial growth to three P management strategies: conventional surface applied, incorporated into the soil, and delaying P applications by 30 days. Results from these experiments indicated rice fields that received conventional surface-applied P fertilizer had 4–8 times more algal/cyanobacterial biomass and 3–11 times higher concentrations of soluble reactive phosphate (SRP) than those in which P fertilizer was incorporated or delayed. Laboratory experiments evaluated the ability of field water to support growth of Nostoc spongiaeforme. Results indicate that water from the incorporated or delayed P application fields was P limited for N. spongiaeforme growth. Water from the surface-applied fields was not P limited. Enclosure experiments evaluated the effects of delayed P applications on algal/cyanobacterial biomass and rice yields. Algal/cyanobacterial cover and biomass increased in enclosures which received added P. Soluble reactive phosphate concentrations were also significantly greater in these enclosures. Delaying the application by up to 28 days did not reduce rice yields in the enclosures. One management implication is that reducing SRP concentrations early in the season in rice field water will result in reduced algal/cyanobacterial biomass. Strategies to reduce water SRP include incorporating fertilizer P or delaying the P application by up to 30 days.

Development of the DET technique for high-resolution determination of soluble reactive phosphate profiles in sediment pore waters

The DET (diffusive equilibrium in thin films) technique is developed to measure soluble reactive phosphate (SRP) profiles in sediment pore waters at a millimetre resolution. The analytical procedure includes equilibration of the gels in sediments, section of the gels after retrieval from the sediments, back elution of phosphorus in the gels, and analysis of SRP in the eluents. Recovery of phosphorus is improved from back elution with 0.25 M nitric acid relative to deionised water. SRP concentrations in pore waters of different sediments measured by DET probes agree well with those directly measured by the colorimetric method. Pore water profiles obtained simultaneously using gel probes and other techniques (including Rhizon and dialysis peeper) also show comparability at similar resolutions. The DET probes were used to investigate pore water SRP profiles in the sediments of two contrasting regions (algal-dominated and macrophyte-dominated) in Lake Taihu. An increasingly upward movement of SRP was observed in subsurface pore waters of the algal-dominated region coupled with an increase in water temperature from March to May. Peak-shape distribution of SRP and horizontal heterogeneity was observed in pore waters of the macrophyte-dominated region, which is most likely caused by the activity of submerged macrophyte roots.

Surface Run-Off Water Quality from Agricultural Lands and Residential Areas

This study was conducted to characterize surface run-off water quality from sugar cane fields, pasturelands and residential areas, and to assess the effectiveness of best management practices (BMPs) in controlling non-point source pollution. From October 2002 to September 2005, the five-day biological oxygen demand (BOD5), total suspended solids (TSS), nitrate/nitrite-N (NO3/NO2-N), soluble reactive phosphate (SRP), total phosphorus (TP), total nitrogen (TN) and pH were determined in surface run-off water from two sugar cane fields, two pasturelands and two residential areas in south-western Louisiana. Faecal coliform counts were carried out on run-off samples from the two pasturelands. The BMPs implemented in one of the sugar cane fields included drop-pipe structures, nutrient management, reduced tillage and the application of herbicides to eliminate summer cultivations, while those implemented in one of the pasturelands included drop-pipe structures, cross-fencing, water points, nutrient management, improved forage planting and managed rotational grazing. Average TSS concentration in surface run-off from the sugar cane fields was significantly higher than the average TSS concentration in the surface run-off from the pastureland and residential areas. Average BOD5 concentrations in surface run-off from the sugar cane fields and pasturelands were significantly higher than the average BOD5 concentration in surface run-off from the residential site. Average TN and NO3/NO2-N concentrations in surface run-off from the sugar cane fields were significantly higher than the average concentration for the pasturelands and residential areas surface run-off. Average TP and SRP concentrations in surface run-off from the pasturelands were significantly higher than the average TP and SRP concentrations in surface run-off from the sugar cane fields and residential areas. The BOD5 was significantly positively correlated with TSS, TN, TP, SRP and NO3/NO2-N. Surface run-off from the sugar cane field with BMPs showed relatively lower median values of TN, TP, NO3/NO2-N and SRP and a slightly higher BOD5 value than the surface run-off from the sugar cane field without BMPs. Similarly, the surface run-off from pastureland with BMPs showed lower median values for TSS, TN and NO3/NO2-N than the surface run-off from pastureland without BMPs.

Interferences in the analysis of nanomolar concentrations of nitrate and phosphate in oceanic waters

This paper reports on investigations into interferences with the measurements of nanomolar nitrate + nitrite and soluble reactive phosphate (SRP) in oceanic surface seawater using a segmented continuous flow autoanalyser (SCFA) interfaced with a liquid-waveguide capillary flow-cell (LWCC). The interferences of silicate and arsenate with the analysis of SRP, the effect of sample filtration on the measurement of nanomolar nitrate + nitrite and SRP concentrations, and the stability of samples during storage are described. The investigation into the effect of arsenate (concentrations up to 100 nM) on phosphate analysis (concentrations up to 50 nM) indicated that the arsenate interference scaled linearly with phosphate concentrations, resulting in an overestimation of SRP concentrations of 4.6 ± 1.4% for an assumed arsenate concentration of 20 nM. The effect of added Si(OH) 4 was to increase SRP signals by up to 36 ± 19 nM (at 100 μM Si(OH) 4). However, at silicate concentrations below 1.5 μM, which are typically observed in oligotrophic surface ocean waters, the effect of silicate on the phosphate analysis was much smaller (≤0.78 ± 0.15 nM change in SRP). Since arsenate and silicate interferences vary between analytical approaches used for nanomolar SRP analysis, it is important that the interferences are systematically assessed in any newly developed analytical system. Filtration of surface seawater samples resulted in a decrease in concentration of 1.7–2.7 nM (±0.5 nM) SRP, and a small decrease in nitrate concentrations which was within the precision of the method (±0.6 nM). A stability study indicated that storage of very low concentration nutrient samples in the dark at 4 °C for less than 24 h resulted in no statistically significant changes in nutrient concentrations. Freezing unfiltered surface seawater samples from an oligotrophic ocean region resulted in a small but significant increase in the SRP concentration from 12.0 ± 1.3 nM ( n = 3) to 14.7 ± 0.6 nM ( n = 3) (Student's t-test; p = 0.021). The corresponding change in nitrate concentration was not significant (Student's t-test; p > 0.05).

Nutrient flux, uptake, and transformation in a spring-fed stream in the Missouri Ozarks, USA

We examined nutrient flux, uptake, and transformation along a spring-fed stream in the Ozark region of Missouri, USA, over the year 2006. Water in Mill Creek originates from several springs, with a single spring contributing over 90% of the stream discharge during much of the year of study. Soluble reactive phosphate concentrations were usually low (<10 μg L−1) along Mill Creek, but peaked during high discharge. Concentrations of dissolved inorganic nitrogen (DIN) were relatively high in the spring water, mainly as nitrate, but usually declined across a small pond and the 10-km length of Mill Creek. During low flows in summer and early autumn, the stream removed over 300 μg L−1 of DIN over its 10-km length, or about 80% of the initial amount. DIN retention along the stream, as a percentage of the DIN upstream, was related mainly to discharge, with higher flows having much higher DIN concentrations. The net uptake rate of DIN uptake was 0.91 μg m−2 s−1 in the stream during summer baseflow. The uptake rate declined downstream for different reaches and was closely related to DIN concentration. In experimental channels, uptake by epilithic algae was one significant sink for nitrate-N in Mill Creek. In 2006, inorganic nutrient export during a single day after a spring storm was similar to export during 40–100 days of low flow conditions in summer and early autumn. Our results suggest that significant nutrient retention can occur during baseflow periods via biological uptake, whereas substantial export occurs during high flow conditions.

Differences in the Soluble, Residual Phosphate Concentrations at Which Coastal Phytoplankton Species Up-regulate Alkaline-Phosphatase Expression, as Measured By Flow-Cytometric Detection of ELF-97® Fluorescence

The enzyme-labeled fluorescence (ELF-97®) substrate produces an insoluble, fluorescent yellow-green product at the site of alkaline-phosphatase (AP) activity. Fifteen coastal phytoplankton species were tested to determine if AP activity could be detected in phosphate- depleted media. All species tested, except Synechococcus bacillaris, expressed AP activity. Subsequently, threshold concentrations of soluble reactive phosphate (SRP) at which AP activity could be detected by ELF-97® were deter- mined for Chaetoceros neogracile, Chlorella autotrophica, Isochrysis sp., Prorocentrum minimum ,a ndTetraselmis chui. Microalgal species differed significantly in the SRP con- centration at which AP activity was first detectable (10.1- 16.4 µM), well above concentrations normally considered limiting for phytoplankton. P. minimum began to express AP activity at a higher SRP concentration than the other algal species; this may be attributable to a relatively high DNA/cell ratio in P. minimum, compared to the other phytoplankton. Thus, phytoplankton species may respond to phosphorus deficiency at high SRP concentrations.

Manual composite sampling in edge-of-field surface runoff for assessing nonpoint source pollution from agricultural lands and residential areas

While there are several surface water quality sampling techniques such as flow-interval, time-interval, and composite sampling, it is still a challenging task to select the appropriate sampling technique for edge-of-field surface runoff water quality monitoring. We hypothesized that manual composite sampling gives comparable results with discrete flow-paced sampling for edge-of-field surface runoff water quality. We collected discrete flow-paced and manual composite surface runoff water samples from sugarcane (<i>Saccharum officinarum</i> L.) fields, pasture lands, and residential areas from October 2002 to October 2003 and analyzed for total suspended solids (TSS), total combustible solids (TCS), five-day Biological Oxygen Demand, nitrate/nitrite-nitrogen (NO₃/NO₂-N), soluble reactive phosphate (SRP), total phosphorus (TP), total nitrogen (TN), and pH in the Vermilion-Teche River Basin in Southwestern Louisiana. Overall, compared to the flow-paced sampling, average five-day Biological Oxygen Demand, TSS, TCS, SRP, TP, NO₃/NO₂-N, and TN concentrations using composite sampling were lower by 4.3%, 8.1%, 8.2%, 9.5%, 4.1%, 36.8%, and 8.2%, respectively. As expected, the constituent concentrations with the flow-paced sampling and the composite sampling were significantly (α = 0.05) positively correlated. Although TSS, TCS, and SRP concentrations slightly declined with flow levels and TP, NO₃/NO₂-N, and TN concentrations showed a general trend of slight increase from 15,142 L (4,000 gal) to 227,125 L (60,000 gal), correlation analysis of the pooled dataset showed no significant correlation (α = 0.05) between flow level and water quality constituents in this study. Similarly, no significant differences were found on event loads of TSS, TCS, SRP, TP, NO₃/NO₂-N, and TN calculated from flow-paced sampling and manual composite sampling strategies. Therefore, manual composite sampling is suggested over flow-paced sampling for edge-of-field water quality monitoring in agricultural lands and residential areas because, while producing comparable results, it reduces the cost of laboratory determination.

Hurricane Katrina induced nutrient runoff from an agricultural area to coastal waters in Biscayne Bay, Florida

Water quality surveys conducted in Biscayne Bay, Florida, indicated enhanced nutrient input coupled with increased runoff as a result of precipitation associated with Hurricane Katrina. Nutrient concentrations before Katrina ranged from 0.06–24.2 μM (mean 3.3 μM) for nitrate and 0.01–0.18 μM (mean 0.1 μM) for soluble reactive phosphate. Five days after Katrina, nitrate concentrations ranged from 0.87–80.0 μM (mean 17.0 μM), with a bay-wide mean increase of 5.2-fold over pre-hurricane levels. Soluble reactive phosphate concentrations ranged from 0.07–0.62 μM (mean 0.2 μM), with a bay-wide mean increase of 2-fold over pre-hurricane levels. The maximum concentrations for both nitrate and soluble reactive phosphate were found at a water quality monitoring station near the mouth of Mowry Canal, which drains an agricultural area in the southern Biscayne Bay watershed near Homestead, Florida. At this station, nitrate and soluble reactive phosphate concentrations increased 7- and 10-fold, respectively. Storm-induced fertilizer runoff from this agricultural area caused a bay-wide increase in nutrient concentrations after Hurricane Katrina. Nutrient concentrations in the bay returned to pre-hurricane levels within three months after Hurricane Katrina, showing the resiliency of the Biscayne Bay ecosystem.

Determination of soluble reactive phosphorus in porewaters of sediments using the technique of diffusive equilibration in thin films

沉积物间隙水溶解态反应性磷(SRP)是反映沉积物磷地球化学特征的敏感指标,对其高分辨率获取一直是难点.基于薄膜扩散平衡(DET)原理,以琼脂糖为原料制备薄膜,通过平衡、切片、提取、测定等步骤,获得溶解态反应性磷的含量信息.实验确定薄膜在磷溶液中的平衡时间为24h,通过0.25mol/L硝酸提取16h可将薄膜萃取的磷提取完全.利用DET技术对不同沉积物间隙水SRP进行了分析,与实际浓度的差异在±5%以内;对沉积物剖面的分析结果与Rhizon、微型Peeper等采样技术基本一致,垂直分辨率可达到3mm左右.利用DET技术对太湖草型和藻型湖区沉积物间隙水SRP进行了分析,发现草型湖区间隙水剖面SRP呈峰形分布,且横向空间分异明显;藻型湖区间隙水SRP随沉积深度的增加呈升高趋势,扩散梯度随水温升高而增强.;Distribution of soluble reactive phosphate (SRP) in pore waters is a sensitive indicator showing geochemical properties ofphosphorus in sediments. Concentration of SRP in synthetic solutions was obtained based on the principle of diffusive equilibration inthin films (DET). Analytical procedure generally includes equilibration of the gels in solutions or pore waters, section of the gels afterretrieval, back elution of phosphorus in the gels, and analysis of SRP in the eluents. Equilibrium and extraction times weredetermined at 24h and 16h, respectively, with 0.25mol/L HNO₃ used as an extractant. Concentrations of SRP in pore waters ofdifferent sediments measured by using the established DET technique agree well with its actual values, and the variations aregenerally within ±5%. Analytical results for sediment profiles with this technique, which has a vertical resolution at about 3mm, alsoshow comparison with those using sampling techniques of Rhizon and Mini-Peeper. The established DET technique was used tomeasure SRP profiles in sediments of macrophyte- and algal-dominated regions in Lake Taihu. Peak-shape distribution and horizontalheterogeneity of SRP were observed in macrophyte-dominated region, while an upward and increasing movement of SRP wasobserved in algal-dominated region with an increase in water temperature.

Nitrogen and oxygen isotopic signatures of subsurface nitrate seaward of the Florida Keys reef tract

Hydrographic and nutrient structure and the nitrogen and oxygen isotopic compositions (d15N and d18O) of the nitrate pool seaward of the Florida Keys reef tract were measured in Summer 2003. Nitrate and soluble reactive phosphate concentrations were tightly associated with depth and temperature and were close to 0 in surface waters, increased to 2–10 µmol L−1 and 0.1–1.0 µmol L−1, respectively, at intermediate depths associated with the thermocline and 15–25 µmol L−1 and 1.0–1.5 µmol L−1, respectively, in deeper water. Ammonium concentrations were low (0–0.6 µmol L−1) at all depths. Dissolved organic carbon concentrations ranged from 70–120 µmol L−1 near the surface to 40–60 µmol L−1 below the thermocline. Mean nitrate δ15N was 4.78% (±0.05) overall and varied from 4.24%(±0.07) within the chlorophyll maximum layer at 50–70 m depth to 5.26% (±0.05) below the thermocline at 150–242 m depth. Mean δ18O mean was 3.26% (±0.08) and varied from 4.89% (±0.14) within the chlorophyll maximum layer to 3.02% (±0.07) below the thermocline. These observations suggest an oceanic, deep‐water nitrate source below the thermocline, a mix of sources from upwelling and N2 fixation, and the effects of fractionation associated with uptake by primary producers within the thermocline. The water column nitrate isotopic data support the general hypothesis that primary producers on the Florida Keys reef tract directly utilize the transiently available subsurface nitrate pool.