Soluble Reactive Phosphate Research Articles

Hydrography and nutrient dynamics in the Northern South China Sea Shelf-sea (NoSoCS)

The hydrographic characteristics and the distributions of nitrate+nitrite, or (N+N), and soluble reactive phosphate, or SRP, in the Northern South China Sea Shelf-sea (NoSoCS) were determined in four transects across the shelf in the summer of 2010 and in two transects in the winter of 2011. The NoSoCS may be sub-divided into the inner shelf, the middle shelf and the outer shelf at water depths of <40m, 40–90m and 90–120m, respectively. The water in the inner shelf is colder and its concentrations in the nutrients and chlorophyll-a (Chl_a) are higher in both seasons while the water in the outer shelf is warmer and its concentrations are lower. With depth, since the mixed layer depth in the NoSoCS in the winter (~70m) and in the summer (~40m) are both shallower than the shelf break depth (~120m), the colder and relatively nutrient-rich upper thermocline-upper nutricline water in the open South China Sea (SCS) can freely extend into the NoSoCS to become its bottom water. This is a distinguishing characteristic of the NoSoCS as, unlike many of the more extensively studied temperate shelf-seas, vertical mixing within the NoSoCS, rather than shelf-edge processes such as upwelling, is the primary mechanism for bringing the nutrients from the sub-surface in the adjoining northern SCS to its mixed layer for supporting primary production. Four processes that may contribute to this vertical mixing in the NoSoCS include: shelf-wide winter surface cooling and convective mixing; the actions of internal waves which probably occur in both seasons along the entire outer shelf; wind and topographically induced coastal upwelling in the summer off Shantou at the northwestern corner of the NoSoCS; and winter formation of bottom water at the outer portion of the inner shelf and the inner portion of the middle shelf. The density of this bottom water formed in the winter of 2011 was equivalent to the density at ~120m in the open SCS so that it could cascade across the shelf and contribute to not only vertical mixing but also in cross shelf mixing and the ventilation of the upper thermocline and nutricline of the open SCS. An enrichment in (N+N) over SRP, where (N+N)/SRP exceeded the Redfield ratio of 16 and [N+N]ex>0, was found when salinity dropped below about 33. In these fresher waters, which were found exclusively in the inner shelf during this study, SRP potentially could become the limiting nutrient.

Key respiratory genes elucidate bacterial community respiration in a seasonally anoxic estuary.

Intense annual spring phytoplankton blooms and thermohaline stratification lead to anoxia in Chesapeake Bay bottom waters. Once oxygen becomes depleted in the system, microbial communities use energetically favourable alternative electron acceptors for respiration. The extent to which changes in respiration are reflected in community gene expression have only recently been investigated. Metatranscriptomes prepared from near-bottom water plankton over a 4-month time series in central Chesapeake Bay demonstrated changes consistent with terminal electron acceptor availability. The frequency of respiration-related genes in metatranscriptomes was examined by BLASTx against curated databases of genes intimately and exclusively involved in specific electron acceptor utilization pathways. The relative expression of genes involved in denitrification and dissimilatory nitrate reduction to ammonium were coincident with changes in nitrate, nitrite and ammonium concentrations. Dissimilatory iron and manganese reduction transcript ratios increase during anoxic conditions and corresponded with the highest soluble reactive phosphate and manganese concentrations. The sulfide concentration peaked in late July and early August and also matched dissimilatory sulfate reduction transcript ratios. We show that rather than abrupt transitions between terminal electron acceptors, there is substantial overlap in time and space of these various anaerobic respiratory processes in Chesapeake Bay.

Nutrient uptake dynamics across a gradient of nutrient concentrations and ratios at the landscape scale

AbstractUnderstanding interactions between nutrient cycles is essential for recognizing and remediating human impacts on water quality, yet multielemental approaches to studying nutrient cycling in streams are currently rare. Here we utilized a relatively new approach (tracer additions for spiraling curve characterization) to examine uptake dynamics for three essential nutrients across a landscape that varied in absolute and relative nutrient availability. We measured nutrient uptake for soluble reactive phosphorous, ammonium‐nitrogen, and nitrate‐nitrogen in 16 headwater streams in the Catskill Mountains, New York. Across the landscape, ammonium‐nitrogen and soluble reactive phosphorus had shorter uptake lengths and higher uptake velocities than nitrate‐nitrogen. Ammonium‐nitrogen and soluble reactive phosphorus uptake velocities were tightly correlated, and the slope of the relationship did not differ from one, suggesting strong demand for both nutrients despite the high ambient water column dissolved inorganic nitrogen: soluble reactive phosphorus ratios. Ammonium‐nitrogen appeared to be the preferred form of nitrogen despite much higher nitrate‐nitrogen concentrations. The uptake rate of nitrate‐nitrogen was positively correlated with ambient soluble reactive phosphorus concentration and soluble reactive phosphorus areal uptake rate, suggesting that higher soluble reactive phosphorus concentrations alleviate phosphorus limitation and facilitate nitrate‐nitrogen uptake. In addition, these streams retained a large proportion of soluble reactive phosphorus, ammonium‐nitrogen, and nitrate‐nitrogen supplied by the watershed, demonstrating that these streams are important landscape filters for nutrients. Together, these results (1) indicated phosphorus limitation across the landscape but similarly high demand for ammonium‐nitrogen and (2) suggested that nitrate‐nitrogen uptake was influenced by variability in soluble reactive phosphorus availability and preference for ammonium‐nitrogen.

Seasonal shift in community pattern of periphytic ciliates and its environmental drivers in coastal waters of the Yellow Sea, northern China

Ciliates are a primary component of the periphyton microfauna and play a crucial role in the functioning of microbial food webs. Seasonal variation in community structures of periphytic ciliate communities was studied, using glass slides as an artificial substratum, during a 1-year cycle (August 2011–July 2012) in coastal waters of the Yellow Sea, northern China. Samples were collected monthly at a depth of 1 m from four sampling stations. A total of 144 ciliate species representing 78 genera, 43 families, 17 orders and eight classes were recorded. Among these species, 31 distributed in all four seasons, while 11, 11, 13 and two forms occurred only in spring, summer, autumn and winter season, respectively. The species number and total abundance peaked in spring and autumn, with minimum values in winter. Ciliate community structures differed significantly between seasons, and were significantly correlated with the changes in environmental variables, especially temperature, pH, dissolved oxygen (DO) and the nutrients. Of 36 dominant species (top 15 ranked contributors in each season), nine (e.g. Pseudovorticella paracratera, Trochilia minuta and Zoothamnium sp.) were significantly correlated with pH, DO or nutrients. Species richness, evenness and diversity measures were significantly correlated with temperature, pH, DO or soluble reactive phosphates. Results demonstrated that periphytic ciliates exhibited a clear seasonal variation in community structures in response to environmental conditions and potentially might be used as a robust bioindicator for assessing environmental quality status in coastal waters.

Occurrence of Hirudinea species in a post urban reach of a Patagonian mountain stream

Temporal (May 2005 to February 2006) and habitat distribution (pools and riffles) of Hirudinea species was analyzed at a post urban reach from Esquel stream (Chubut province, Patagonia, Argentina). Site was located 5.7 km downstream a Waste Treatment Plant. Mean values of nutrients: ammonia, nitrates and soluble reactive phosphate, as well water conductivity, turbidity and total suspended solids indicated physical and organic pollution. Leeches assemblage was composed by the glossiphonids: Helobdella scutifera Blanchard, 1900, H. michaelseni (Blanchard, 1900), H. simplex (Moore, 1911), Helobdella sp., H. hyalina Ringuelet, 1942, H. obscura Ringuelet, 1942 and the semiscolecid Patagoniobdella variabilis (Blanchard, 1900). From these H. hyalina and H. obscura are new records for Chubut province. Helobdella hyalina (810 ind.m-2) and H. simplex (465 ind. m-2) clearly dominated the assemblage at the reach. Only H. simplex displayed a spatial preference being significantly more abundant in pools than in riffle habitats (p&lt;0.001). Species recruitment occurred mostly at September, December and March when juveniles were very abundant. Although several species of Helobdella were able to live in the disturbed section of the stream, only H. simplex and H. hyalina sustained large populations at the site and can be considered as tolerant to organic enrichment. This information is valuable to future studies on stream condition assessment in mountainous areas in Patagonia, and in other areas in which these species are present.

Using a Hydroponic System with Tall Fescue to Remove Nitrogen and Phosphorus from Renovated Turkey Processing Wastewater

Abstract. Rising nitrogen and phosphorus related nutrient pollution in different aquifers, as indicated by the deterioration of water quality, triggered this study. The aim of this study was to use commercially valuable ornamental plants, such as tall fescue, for wastewater treatment without decreasing the overall treatment efficiencies of a laboratory-scale hydroponic (soilless) system. Renovated turkey processing wastewater, from a sand bioreactor treatment system at a turkey processing plant, was used in this experiment. Nitrate and phosphate were measured in influent and effluent of the hydroponic system to evaluate the nutrient removal efficiency. Tall fescue was cultured on media consisting of perforated plastic plates and one layer of burlap. Water samples were tested at 12 h intervals under 2-day hydraulic retention times. Average removals of 53% nitrate and 68% soluble reactive phosphate were achieved at 48 h under 2-day hydraulic retention time. The 2-day retention time was optimal for nutrient removal at 22 to 28 days of growth. The plant nutrient content was also determined. The tall fescue hydroponic system, including possible microbial participation, accounted on average for 14% nitrate-N and 42% P removal. Improvement in the efficiencies could come from a better understanding of the biological mechanisms and controls of nutrient removal.

Influence of cyanobacteria blooms on sediment biogeochemistry and nutrient fluxes

To explore the influence of cyanobacteria blooms on internal nutrient loading and sediment biogeochemistry, we conducted a 3 yr (2008–2010) field investigation in the upper Sassafras River, a shallow tidal freshwater tributary of Chesapeake Bay, Maryland. During 2010 a dense diazotrophic cyanobacteria bloom was accompanied by abnormally high pH (9.0–10.5) and supersaturated oxygen throughout the summer. With the persistence of high pH in the water column and organic matter inputs from sedimented phytoplankton detritus, flux rates of NH+4 and soluble reactive phosphate were significantly higher during the summer of the bloom year than the same period in nonbloom years. Although low summer N2‐N flux rates generally coincided with reduced water‐column NO−3 concentrations, the efficiency of nitrification was constrained by elevated pH that converted NH+4 to more toxic NH3. Denitrification was subsequently limited by nitrate supply, elevated pH, and the deepening of the oxic layer in the sediment. During blooms, we observed increases in bioavailable nutrient release from the sediment, coupled with decreases in inorganic N : P flux ratios and inhibition of N2 loss from the ecosystem. These changes in sediment nutrient recycling created positive feedbacks that may have fueled the prolonged blooms and selectively fostered growth of diazotrophic cyanobacteria.

The Response of Macrophytes to Nutrients and Implications for the Control of Phytoplankton Blooms in East Taihu Lake, China

When macrophytes are growing in the eutrophicated aquatic ecosystem, the vegetation induces important effects to the water quality and phytoplankton concentrations in the water which affected by macroscopic physical, chemical and biological processes and the effects are the results of direct and indirect interactions of the aquatic plants and water body. The interactions between macrophytes, nutrients and phytoplankton blooms were examined in the water and sediments of a shallow, eutrophic and typical East Taihu, China. The importance of macrophytes as a sink for nutrients, and the inhibitory effect of macrophytes on phytoplankton bloom potential were assessed through three different seasons. Luxuriant aquatic plants growth in this system led to decrease available nutrients for phytoplankton and prevented bloom development. Uptake of N and P by aquatic plants accounted for a major portion of the observed N and P loss from the water column and sediments. Luxury uptake of N and P were indicated by high biomass and tissues N and P concentrations, indicating the capacity of macrophytes to act as a nutrient sink in midsummer. Dissolved inorganic N (DIN) and soluble reactive phosphorous (SRP) in water were reduced in midsummer in the presence of macrophytes. The use of macrophytes to reduce the nutrients in water system and thereby inhibit freshwater phytoplankton blooms should be considered as an effective management strategy in shallow eutrophicated lakes. As aquatic macrophytes also develops considerable indirect effects that could have a vital impact than the direct uptake the nutrients into the plant biomass.

Evaluation of vertical and horizontal changes in community structure of zooplankton in a deep dam lake

The purpose of this study was to describe the horizontal and vertical distributions of the zooplankton community structure in Karakaya Dam Lake. Rotifers were numerically dominant (81.89%) in the community during the study period; they were followed by Copepoda (10.32%) and Cladocera (7.79%). In the metalimnetic maximum oxygen zone between 5 and 10 m, cladocerans made up 70.1% of the total number of zooplankton in June and 27.3% of the total number of zooplankton in November. Oxygen values decreased at 10 and 15 m in September and November. While the abundance of rotifers and cladocerans decreased as well, cyclopoids increased (60% of total zooplankton at 10 m). Nitrogen and soluble reactive phosphate were at low concentrations. Relationships among zooplankton, abundance, and environmental factors were analyzed using the unweighted pair-group method using arithmetic averages (UPGMA) and canonical correspondence analysis (CCA). UPGMA cluster analysis was used to illustrate unimodal species distribution by classification into 2 groups. Eigenvalues of axes clarified 42.7% of the cumulative variance in species data and 62.9% of the relationship between species and environmental data in the CCA. Many zooplankton species, rather tolerant to different environmental conditions, are good indicators for water quality and can be used for the biomonitoring of water ecosystems.

Seasonal and spatial variations in limnological conditions of a floodplain lake (lake Catalão) connected to both the Solimões and Negro Rivers, Central Amazonia

Lakes play an important role in biogeochemical, ecological and hydrological processes in the river-floodplain system. The aim of this study was to evaluate the dynamics of the limnological conditions of Catalão Lake, an Amazon floodplain lake. Thus, some of the main limnological environment variables (O2, temperature, pH, nutrient, electrical conductivity) of the Catalão Lake were analyzed under temporal and spacial scales. The study was conducted between November/2004 and August/2005. Sampling excursion were carried out every three months; one excursion for each of the four different hydrological periods (low water, rising water, high water and falling water). Sampling points were chosen so that it could be obtained a gradient of the distance from Negro River. Limnological profiles in Catalão Lake showed generally acidic to slightly alcaline water, with low levels of dissolved oxygen and low concentrations of soluble reactive phosphorous. The Negro River seems to exert the main influence during the rising water period, while the Solimões River is the principal controlling river during peak water. The Principal Component Analysis (PCA) grouped the seasonal collections by hydrological period, showing the formation of a north-south spatial gradient within the lake in relation to the limnological variables. Multivariate dispersion analysis based on distance-to-centroid method demonstrated an increase in similarity over the course of the hydrological cycle, as the lake was inundated in response to the flood pulse of the main river channels. However, the largest spatial homogeneity in the lake was observed in the epilimnion layer, during the falling water period. The daily analysis of variation indicated an oligomitic pattern during the years in which the lake was permanently connected to the Negro River. Although Catalão Lake receives large quantities of both black water from the Negro River and sediment-filled water from the Solimões River, the physical and chemical characteristics of the lake are more similar to those of the Solimões (várzea lake) than the Negro (blackwater lake).

Use of biofilm-dwelling ciliate communities to determine environmental quality status of coastal waters

It has increasingly been recognized that the ecological features of protozoan communities have many advantages as a favorable bioindicator to evaluate environmental stress and anthropogenic impact in many aquatic ecosystems. The ability of biofilm-dwelling ciliate communities for assessing environmental quality status was studied, using glass slides as an artificial substratum, during a 1-year cycle (August 2011–July 2012) in coastal waters of the Yellow Sea, northern China. The samples were collected monthly at a depth of 1m from four sampling stations with a spatial gradient of environmental stress. Environmental variables, e.g., salinity, dissolved oxygen (DO), chemical oxygen demand (COD), nitrate nitrogen (NO3–N), ammonium nitrogen (NH4–N) and soluble reactive phosphates (SRP), were measured synchronously for comparison with biotic parameters. Results showed that: (1) the community structures of the ciliates represented significant differences among the four sampling stations; (2) spatial patterns of the ciliate communities were significantly correlated with environmental variables, especially COD and the nutrients; (3) five dominant species (Hartmannula angustipilosa, Metaurostylopsis sp.1, Discocephalus ehrenbergi, Stephanopogon minuta and Pseudovorticella paracratera) were significantly correlated with nutrients or COD; and (4) the species richness measure was significantly correlated with the nutrient NO3–N. It is suggested that biofilm-dwelling ciliate communities might be used as a potentially robust bioindicator for discriminating environmental quality status in coastal waters.

Impact of the Kuroshio intrusion on the nutrient inventory in the upper northern South China Sea: insights from an isopycnal mixing model

Abstract. Based on four cruises covering a seasonal cycle in 2009–2011, we examined the impact of the Kuroshio intrusion, featured by extremely oligotrophic waters, on the nutrient inventory in the central northern South China Sea (NSCS). The nutrient inventory in the upper 100 m of the water column in the study area ranged from ∼200 to ∼290 mmol m−2 for N + N (nitrate plus nitrite), from ∼13 to ∼24 mmol m−2 for soluble reactive phosphate and from ∼210 to ∼430 mmol m−2 for silicic acid. The nutrient inventory showed a clear seasonal pattern with the highest value appearing in summer, while the N + N inventory in spring and winter had a reduction of ∼13 and ∼30%, respectively, relative to that in summer. To quantify the extent of the Kuroshio intrusion, an isopycnal mixing model was adopted to derive the proportional contribution of water masses from the SCS proper and the Kuroshio along individual isopycnal surfaces. The derived mixing ratio along the isopycnal plane was then employed to predict the genuine gradients of nutrients under the assumption of no biogeochemical alteration. These predicted nutrient concentrations, denoted as Nm, are solely determined by water mass mixing. Results showed that the nutrient inventory in the upper 100 m of the NSCS was overall negatively correlated to the Kuroshio water fraction, suggesting that the Kuroshio intrusion significantly influenced the nutrient distribution in the SCS and its seasonal variation. The difference between the observed nutrient concentrations and their corresponding Nm allowed us to further quantify the nutrient removal/addition associated with the biogeochemical processes on top of the water mass mixing. We revealed that the nutrients in the upper 100 m of the water column had a net consumption in both winter and spring but a net addition in fall.

Phytoplankton patchiness during spring intermonsoon in western coast of South China Sea

Jet-like phytoplankton blooms usually occur off the southwestern coast of the South China Sea (SCS) caused by strong winds during summer monsoons. However a jet-like phytoplankton patch was observed in the western SCS in the spring intermonsoon of 2010 in both field and remote sensing data. The present study investigated the biological processes associated with this spring phytoplankton patchiness. The data showed that chlorophyll a concentrations increased in the surface water, extending out to the SCS, and the depth of the subsurface chlorophyll maximum uplifted from 75m to 50m depth; low dissolved oxygen, low pH and nutrient enrichment (nitrate+nitrite and soluble reactive phosphate) were observed in the subsurface water (50 to ~200m depth). Data analysis showed that variations in chlorophyll a, nutrients and temperature in the water column were related to wind-stress curl: the spatial distribution pattern and vertical structure of the phytoplankton patchiness were controlled by vertical flux of nutrients caused by curl-driven upwelling through Ekman pumping. There was a high correlation between chlorophyll a concentration and wind-stress curl where the influence of nutrient influx from the coast was limited. This study shows the importance of wind-stress curl in providing nutrients to support phytoplankton growth during the spring intermonsoon along the western coast of SCS. It may help to better understand the role of wind in marine biological processes.

Multivariate benthic ecosystem functioning in the Arctic – benthic fluxes explained by environmental parameters in the southeastern Beaufort Sea

Abstract. The effects of climate change on Arctic marine ecosystems and their biogeochemical cycles are difficult to predict given the complex physical, biological and chemical interactions among the ecosystem components. We studied benthic biogeochemical fluxes in the Arctic and the influence of short-term (seasonal to annual), long-term (annual to decadal) and other environmental variability on their spatial distribution to provide a baseline for estimates of the impact of future changes. In summer 2009, we measured fluxes of dissolved oxygen, nitrate, nitrite, ammonia, soluble reactive phosphate and silicic acid at the sediment–water interface at eight sites in the southeastern Beaufort Sea at water depths from 45 to 580 m. The spatial pattern of the measured benthic boundary fluxes was heterogeneous. Multivariate analysis of flux data showed that no single or reduced combination of fluxes could explain the majority of spatial variation, indicating that oxygen flux is not representative of other nutrient sink–source dynamics. We tested the influence of eight environmental parameters on single benthic fluxes. Short-term environmental parameters (sinking flux of particulate organic carbon above the bottom, sediment surface Chl a) were most important for explaining oxygen, ammonium and nitrate fluxes. Long-term parameters (porosity, surface manganese and iron concentration, bottom water oxygen concentrations) together with δ13Corg signature explained most of the spatial variation in phosphate, nitrate and nitrite fluxes. Variation in pigments at the sediment surface was most important to explain variation in fluxes of silicic acid. In a model including all fluxes synchronously, the overall spatial distribution could be best explained (57%) by the combination of sediment Chl a, phaeopigments, δ13Corg, surficial manganese and bottom water oxygen concentration. We conclude that it is necessary to consider long-term environmental variability along with rapidly ongoing environmental changes to predict the flux of oxygen and nutrients across Arctic sediments even at short timescales. Our results contribute to improve ecological models predicting the impact of climate change on the functioning of marine ecosystems.

The fate of riverine nutrients on Arctic shelves

Abstract. Present and future levels of primary production (PP) in the Arctic Ocean (AO) depend on nutrient inputs to the photic zone via vertical mixing, upwelling and external sources. In this regard, the importance of horizontal river supply relative to oceanic processes is poorly constrained at the pan-Arctic scale. We compiled extensive historical (1954–2012) data on discharge and nutrient concentrations to estimate fluxes of nitrate, soluble reactive phosphate (SRP), silicate, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), particulate organic nitrogen (PON) and particulate organic carbon (POC) from 9 large Arctic rivers and assess their potential impact on the biogeochemistry of shelf waters. Several key points can be emphasized from this analysis. The contribution of riverine nitrate to new PP (PPnew) is very small at the regional scale (&lt; 1% to 6.7%) and negligible at the pan-Arctic scale (&lt; 0.83%), in agreement with recent studies. By consuming all this nitrate, oceanic phytoplankton would be able to use only 14.3% and 8.7–24.5% of the river supply of silicate at the pan-Arctic and regional scales, respectively. Corresponding figures for SRP are 28.9% and 18.6–46%. On the Beaufort and Bering shelves, riverine SRP cannot fulfil phytoplankton requirements. On a seasonal basis, the removal of riverine nitrate, silicate and SRP would be the highest in spring and not in summer when AO shelf waters are nitrogen-limited. Riverine DON is potentially an important nitrogen source for the planktonic ecosystem in summer, when ammonium supplied through the photoammonification of refractory DON (3.9 × 109 mol N) may exceed the combined riverine supply of nitrate and ammonium (3.4 × 109 mol N). Nevertheless, overall nitrogen limitation of AO phytoplankton is expected to persist even when projected increases of riverine DON and nitrate supply are taken into account. This analysis underscores the need to better contrast oceanic nutrient supply processes with the composition and fate of changing riverine nutrient deliveries in future scenarios of plankton community structure, function and production in the coastal AO.

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.

Factors Affecting Phosphorous in Groundwater in an Alluvial Valley Aquifer: Implications for Best Management Practices

Many streams in the US are impaired because of high Soluble Reactive Phosphorous (SRP) contributions from agriculture. However, the drivers of ecological processes that lead to SRP loss in baseflow from groundwater are not sufficiently understood to design effective Best Management Practices (BMPs). In this paper, we examine how soil temperature and water table depth influence the SRP concentrations in groundwater for a dairy farm in a valley bottom in the Catskills (NY, USA). Measured SRP concentrations in groundwater and baseflow were greater during the fall, when soil temperatures are warmer, than during winter and spring. The observed concentrations were within the bounds predicted by groundwater temperatures using the Arrhenius equation, except during fall, when concentrations rose above these predictions. These elevated concentrations were likely caused by mineralization and consequent accumulation of phosphorous (P) in summer. In addition, SRP concentrations were greater in near-stream areas, where water tables where higher. In short, SRP concentrations are dependent on temperature, demonstrating the importance of understanding the underlying mechanism of ecological processes. In addition, results suggest BMPs that apply manure on land having a deep groundwater, instead of on land with a shallow water table will lower overall SRP contributions.

Assessment of seasonal and spatial variation of surface water quality, identification of factors associated with water quality variability, and the modeling of critical nonpoint source pollution areas in an agricultural watershed

Surface water quality impairment in agricultural watersheds is a major environmental concern in the United States. To assess seasonal and spatial variability of surface water quality and identify factors associated with surface water quality variability, we monitored surface water quality at seven locations in Bayou Plaquemine Brule Watershed in Louisiana twice monthly from March of 2002 to February of 2008 and performed multivariate analyses of the dataset. Using the Soil and Water Assessment Tool (SWAT) model, we identified critical areas of nonpoint source pollution in the watershed. While temperature, turbidity, dissolved oxygen (DO), conductivity and pH were determined in the field using YSI Sonde (YSI Incorporated, Yellow Springs, Ohio), surface water samples were analyzed for total nitrogen (TN), total phosphorus (TP), nitrate/nitrite-N (NO₃/NO₂-N), soluble reactive phosphate (SRP), total suspended solids (TSS), and five-day biological oxygen demand (BOD₅) in laboratory. The monthly water quality sampling included a regular sampling and an after-rain-event sampling. Average DO for the summer months, March through November, was 4.91 ± 0.08 mg L⁻¹ (4.91 ± 0.08 ppm), while average DO for the winter months, December through February, was 8.32 ± 0.12 mg L⁻¹ (8.32 ± 0.12 ppm). Dissolved oxygen was negatively correlated with TN (<i>r</i> = −0.22, <i>p</i> ≤ 0.001), SRP (<i>r</i> = −0.17, <i>p</i> ≤ 0.001), TP (<i>r</i> = −0.17, <i>p</i> ≤ 0.001), BOD₅ (<i>r</i> = −0.25, <i>p</i> ≤ 0.001), and surface water temperature (<i>r</i> = −0.70, <i>p</i> ≤ 0.001). Turbidity was strongly correlated with TSS (<i>r</i> = 0.59, <i>p</i> ≤ 0.001), suggesting that most turbidity in the water body comes from suspended solids. Similarly BOD₅ was significantly positively correlated with TN (<i>r</i> = 0.43, <i>p</i> ≤ 0.001), NO₃/NO₂-N (<i>r</i> = 0.26, <i>p</i> ≤ 0.001), TP (<i>r</i> = 0.25, <i>p</i> ≤ 0.001), and SRP (<i>r</i> = 0.18, <i>p</i> ≤ 0.001). Results of factor analyses showed sediment, phosphorus (P), nitrogen (N), surface water temperature, dissolved solids, and acidity/alkalinity as the most important factors associated with surface water quality variability in this watershed. Although relatively higher concentrations of sediments, TP, and TN were observed in the upper reaches of the watershed based on water quality monitoring, the SWAT simulation results showed the critical nonpoint source pollution areas of sediment, P, and N in the lower reaches of the watershed. Lower reaches of the watershed have mainly rice and crawfish production, while the upper reaches include primarily sugarcane, pasturelands, and soybean production. Information on seasonal variability of surface water quality, factors associated with surface water quality variability, and the critical areas for nonpoint source pollution will be valuable inputs for developing a watershed management plan for effective nonpoint source pollution control in an agricultural watershed.

Submarine groundwater discharge in a river-dominated Florida estuary

Eutrophication in the coastal zone has largely been driven by changing land use practices that lead to nutrient-enhanced runoff. While in most studies the overland component of this nutrient vector has been well documented, the role of groundwater in coastal nutrient mass balances is often poorly constrained. Here, we used radium isotopes to quantify SGD and associated nutrient fluxes to the Caloosahatchee River estuary (Florida, USA) during the wet and dry seasons of 2009–2010. Like many estuaries worldwide, the nutrient balance and ecology of the Caloosahatchee has been negatively impacted by excessive nutrient-laden runoff from fertilizer use and other anthropogenic sources. A four endmember mixing model was used to quantify the magnitude of SGD and the relative importance of terrestrial and marine groundwater sources. Terrestrial groundwater comprised 44% of the total SGD in April 2009, but 98–100% of the total groundwater flux during all other time periods. SGD rates were highly seasonal ranging from a low of 8.5×104m3d−1 in April 2010 to a high of 1.3×106m3d−1 in October 2010 (average=4.8±5.5×105m3d−1). For the four time periods, these fluxes ranged from 2 to 140% (average=43%) of the river discharge through Franklin Lock, a water control structure at the head of the estuary and the only previously quantified source of nutrients to the system. The groundwater total dissolved nitrogen (TDN) flux to the estuary averaged 450±490kgd−1 for the four time periods, while dissolved inorganic nitrogen (DIN) and soluble reactive phosphorous (SRP) averaged 241±267kgd−1 and 93±111kgd−1, respectively. On average, the surface water freshwater fluxes for TDN exceeded the SGD fluxes by a factor of 6. However, the SGD fluxes of DIN and SRP, highly bioavailable forms of N and P, were only 3 and 1.5 times lower than the river flux, respectively. The major form of nitrogen carried by groundwater to the estuary was ammonium; this highly labile form of nitrogen is likely rapidly consumed within the estuary by primary producers (both macro- and microalgae). Our results suggest that during extended dry periods when water releases from Franklin Lock are at a minimum, SGD will remain a substantial source of nutrients to the system.

Porewater temporal variability in a wave-impacted permeable nearshore sediment

Porewater samples were collected from a nearshore permeable sediment on Oahu, Hawaii over a variety of surface gravity wave conditions to evaluate the effect of ocean swells and their corresponding bottom currents on porewater dissolved oxygen and inorganic nutrient dynamics. Our results indicate that swells with significant wave heights of ~1.3m, with resulting nearbed velocities reaching at least 0.30ms−1, flush the porewater to a depth of ~7.5cm by enhancing exchange between the upper sediment and the overlying water column. Upper-sediment dissolved oxygen inventories were positively correlated with nearbed velocities, and decline linearly versus time during background conditions following upper-sediment flushing, corresponding to an apparent upper-sediment deoxygenation rate of 0.31mmolm−2d−1. Similarly, upper-sediment nutrient inventories were observed to recover linearly after swell events, resulting in sediment recovery rates for silicate and soluble reactive phosphate of 35μmolm−2d−1 and 3.5μmolm−2d−1, respectively. The observed elemental ratios of regenerated nutrients suggest that the majority of organic matter undergoing remineralization is planktonic in origin. Wave-enhanced exchange is associated with a fluorescence response in the bottom of the overlying water column, suggesting that sediment flushing and subsequent nutrient input to the water column may be important to nutrient budgets and photosynthetic communities in nearshore oligotrophic waters.