Groundwater Nutrient Concentrations Research Articles

From submarine to lacustrine groundwater discharge

Abstract. Submarine groundwater discharge (SGD) and its role in marine nutrient cycling are well known since the last decade. The freshwater equivalent, lacustrine groundwater discharge (LGD), is often still disregarded, although first reports of LGD are more than 50 years old. We identify nine different reasons why groundwater has long been disregarded in both freshwater and marine environments such as invisibility of groundwater discharge, the size of the interface and its difficult accessibility. Although there are some fundamental differences in the hydrology of SGD and LGD, caused primarily by seawater recirculation that occurs only in cases of SGD, there are also a lot of similarities such as a focusing of discharge to near-shore areas. Nutrient concentrations in groundwater near the groundwater–surface water interface might be anthropogenically enriched. Due to spatial heterogeneity of aquifer characteristics and biogeochemical processes, the quantification of groundwater-borne nutrient loads is challenging. Both nitrogen and phosphorus might be mobile in near-shore aquifers and in a lot of case studies large groundwater-borne nutrient loads have been reported.

Groundwater – the disregarded component in lake water and nutrient budgets. Part 2: effects of groundwater on nutrients

AbstractLacustrine groundwater discharge (LGD) transports nutrients from a catchment to a lake, which may fuel eutrophication, one of the major threats to our fresh waters. Unfortunately, LGD has often been disregarded in lake nutrient studies. Most measurement techniques are based on separate determinations of volume and nutrient concentration of LGD: Loads are calculated by multiplying seepage volumes by concentrations of exfiltrating water. Typically low phosphorus (P) concentrations of pristine groundwater often are increased due to anthropogenic sources such as fertilizer, manure or sewage. Mineralization of naturally present organic matter might also increase groundwater P. Reducing redox conditions favour P transport through the aquifer to the reactive aquifer‐lake interface. In some cases, large decreases of P concentrations may occur at the interface, for example, due to increased oxygen availability, while in other cases, there is nearly no decrease in P. The high reactivity of the interface complicates quantification of groundwater‐borne P loads to the lake, making difficult clear differentiation of internal and external P loads to surface water. Anthropogenic sources of nitrogen (N) in groundwater are similar to those of phosphate. However, the environmental fate of N differs fundamentally from P because N occurs in several different redox states, each with different mobility. While nitrate behaves essentially conservatively in most oxic aquifers, ammonium's mobility is similar to that of phosphate. Nitrate may be transformed to gaseous N2 in reducing conditions and permanently removed from the system. Biogeochemical turnover of N is common at the reactive aquifer‐lake interface. Nutrient loads from LGD were compiled from the literature. Groundwater‐borne P loads vary from 0.74 to 2900 mg PO4‐P m−2 year−1; for N, these loads vary from 0.001 to 640 g m−2 year−1. Even small amounts of seepage can carry large nutrient loads due to often high nutrient concentrations in groundwater. Large spatial heterogeneity, uncertain areal extent of the interface and difficult accessibility make every determination of LGD a challenge. However, determinations of LGD are essential to effective lake management. Copyright © 2014 John Wiley & Sons, Ltd.

Using chemical, microbial and fluorescence techniques to understand contaminant sources and pathways to wetlands in a conservation site

Nutrients and faecal contaminants can enter wetland systems in a number of ways, with both biological and potentially human-health implications. In this study we used a combination of inorganic chemistry, dissolved organic matter (DOM) fluorescence and Escherichia coli and total coliform (TC) count techniques to study the sources and multiple pathways of contamination affecting a designated sand dune site of international conservation importance, surrounded by agricultural land. Analysis of stream samples, groundwater and dune slack wetlands revealed multiple input pathways. These included riverbank seepage, runoff events and percolation of nutrients from adjacent pasture into the groundwater, as well as some on-site sources. The combined techniques showed that off-site nutrient inputs into the sand dune system were primarily from fertilisers, revealed by high nitrate concentrations, and relatively low tryptophan-like fulvic-like ratios <0.4Ramanunits (R.U.). The E. coli and TC counts recorded across the site confirm a relatively minor source of bacterial and nutrient inputs from on-site grazers. Attenuation of the nutrient concentrations in streams, in groundwater and in run-off inputs occurs within the site, restoring healthier groundwater nutrient concentrations showing that contaminant filtration by the sand dunes provides a valuable ecosystem service. However, previous studies show that this input of nutrients has a clear adverse ecological impact.

The role of snowmelt runoff on the ocean environment and scallop production in Funka Bay, Japan

This study investigated the role of snowmelt runoff on water circulation, water mass formation, and the production of cultured scallop larvae, as a part of a land-sea linkage, by analyzing hydrological data in conjunction with nutrient data and by conducting sensitivity experiments based on a coupled land-sea model of Funka Bay, Japan, a typical semi-enclosed bay. A comparison between observed data and the simulated runoff showed that, using newly compiled datasets of nutrient concentrations in rivers and groundwater, the model was sufficiently accurate to estimate the terrestrial dissolved inorganic nitrogen (DIN) flux from the river and submarine groundwater discharges (SGDs). The average volume flux from the SGDs accounted for 26% of the riverine runoff flux. The DIN flux from SGDs accounted for a maximum of 40% of the total DIN loading to the bay before the snowmelt period. Sensitivity experiments using an ocean simulation indicated that the freshwater flux supplied by snowmelt runoff not only enhances clockwise circulations along with upwelling along the coast, but also modifies the distributions of wintertime water masses in the bay. However, the snowmelt runoff has little effect on larvae transport since wind forcing, rather than riverine buoyancy, dominates the circulation patterns. The annual density of scallop spat was highly correlated with snowmelt runoffs associated with high DIN concentrations, which suggested that riverine nutrients can increase the biomass of phytoplankton in near-shore seas and improve food availability for scallop spawners, resulting in increased egg production in March to April. Therefore, the nutrient flux from agricultural source areas through the large snowmelt runoff has an important role in larvae production. Land-sea linkages need to be identified to design sustainable and synergetic systems of aquaculture and agriculture for the integrated management of coastal regions.

Stream and shallow groundwater nutrient concentrations in an Ozark forested riparian zone of the central USA

Characterizing spatiotemporal variations in surface water (SW)–shallow groundwater (GW) nutrient concentrations is important to predict stream ecosystem responses to disturbance. Unfortunately, there is a lack of such information from mixed-deciduous semi-karst hydro-geological regions. Nitrate (NO3−), total phosphorous (P), potassium (K) and ammonium (NH4+) concentrations were monitored in a case study between an Ozark stream and riparian hardwood forest GW over the 2011 water year in the central USA. Average SW NO3−, P, K and NH4+ concentrations were 0.53, 0.13, 3.29 and 0.06 mg L−1, respectively. Nine meters from the streambank, average GW NO3− concentration was 0.01 mg L−1, while P, K and NH4+ concentrations were 0.03, 1.7 and 0.04 mg L−1, respectively. Hyperbolic dilution model results indicated that NO3− and K exhibited dilution behavior, while NH4+ had a concentration effect and P was hydrologically constant. Observed seasonal NO3− concentration patterns of winter maxima and summer minima in SW (1.164 and 0.133 mg L−1) and GW (0.019 and 0.011 mg L−1) were supported by previous studies yet exhibited distinct semi-karst characteristics. Results indicate that in addition to relatively low residence time, lower nutrient concentrations in GW (relative to SW) may suggest that shallow GW flow processes are important for vegetation removal and retention of nutrients from streams in semi-karst shallow groundwater systems of the central USA.

Do groundwater dynamics drive spatial patterns of tree density and diversity in Neotropical savannas?

AbstractQuestionsWhat are the temporal and spatial variations of groundwater depth along topographic gradients in Neotropical savannas? Are patterns of tree density and species diversity along topographic gradients in Neotropical savannas controlled by water table depth? Do soil and groundwater nutrient concentrations differ along topographic gradients in Neotropical savannas?LocationFire‐protected savannas of central Brazil.MethodsOver 16 mo, we monitored temporal and spatial variations in groundwater levels using automated submersible pressure transducers installed in ten wells located along two topographic gradients (five wells per gradient) of 950 m and 1703 m in length, representing elevations of 47 and 37 m a.s.l., respectively. We located the wells according to changes in vegetation physiognomies from woody savannas at high elevations, to open shrubby grasslands at low elevations. Along each topographic gradient we determined soil and groundwater nutrient concentrations as well as richness, density, basal diameter and height of trees within two plots of 14 × 14 m (392 m2) adjacent to each well.ResultsAlong the two gradients, groundwater levels exhibited larger fluctuations at lower than at higher elevations where the water table was deeper. Richness, density and diversity of trees decreased significantly at lower elevations where soils were waterlogged during the wet season. Soil pH and soil concentrations of carbon, nitrogen and manganese decreased significantly as elevation increased along the topographic gradients, but soil nutrient concentrations of phosphorus, aluminium and iron did not change with elevation. Groundwater samples contained only trace amounts of nutrients and were poorly correlated with elevation along the topographic gradients.ConclusionsIn Neotropical savannas, the minimum distance between the soil surface and water table depth (reached during the wet season) and the relatively large fluctuations in groundwater limit tree density and diversity at low elevations as savanna trees cannot cope with extended waterlogging during the wet season and with low soil water availability during the dry season. Thus, variations of tree density and diversity along topographic gradients are more related to spatial and temporal variations in water table depth than to soil and groundwater nutrient variations in Neotropical savannas.

Evidence for sensitivity of dune wetlands to groundwater nutrients

Dune slacks are seasonal wetlands, high in biodiversity, which experience considerable within-year and between-year variations in water-table. They are subject to many pressures including climate change, land use change and eutrophication. Despite their biological importance and the threats facing them, the hydrological and nutrient parameters that influence their soil properties and biodiversity are poorly understood and there have been no empirical studies to date testing for biological effects in dune systems resulting from groundwater nutrients at low concentrations. In this study we examined the impact of groundwater nutrients on water chemistry, soil chemistry and vegetation composition of dune slacks at three distance classes (0–150m, 150–300m, 300–450m) away from known (off-site) nutrient sources at Aberffraw dunes in North Wales, whilst accounting for differences in water-table regime. Groundwater nitrate and dissolved inorganic nitrogen (DIN) and soil nitrate and nitrite all had significantly higher concentrations closest to the nutrient source. Multivariate analysis showed that although plant species composition within this site was primarily controlled by water table depth and water table fluctuation, nitrogen from groundwater also influenced species composition, independently of water table and soil development. A model containing all hydrological parameters explained 17% of the total species variance; an additional 7% was explained following the addition of NO3 to this model. Areas exposed to elevated, but still relatively low, groundwater nutrient concentrations (mean 0.204mg/L+/−0.091 of DIN) had greater abundance of nitrophilous species and fewer basipholous species than in areas with lower concentrations. This shows that clear biological impact occurs below previously suggested DIN thresholds of 0.20–0.40 (mg/L).

Effectiveness of natural riparian buffers to reduce subsurface nutrient losses to incised streams

Perennial vegetation borders many incised, perennial streams and rivers in southern Iowa and is assumed to provide a natural riparian buffer against subsurface nutrient losses from shallow groundwater. Questions remain about the effectiveness of these systems near incised channels that cut through nutrient-rich Holocene alluvium underlying the riparian corridors. In this study, riparian groundwater nutrient concentrations were evaluated near an incised stream under four perennial land cover types common to southern Iowa with the objectives to assess how groundwater quality differed by i) distance away from an incised stream and ii) perennial land cover type. Groundwater samples were collected from riparian wells installed 1m, 20m and 40m from an incised channel under four replicated land covers (cool season grass, warm season grass, woods, pasture) on six occasions across the growing season. Results indicate that channel incision lowers water tables in the near-stream zone and maintains more aerobic conditions but did not result in enhanced nitrogen mineralization or leaching to groundwater. Average concentrations of nitrate–nitrogen, phosphorus and dissolved organic carbon were 0.3mg/l, 0.2mg/l and 6mg/l, respectively, with variations due mainly to land cover type and geomorphology. Study results suggest that nutrient losses from perennial buffers in the region do not greatly impact regional water N and P loads although average concentrations in riparian groundwater may exceed proposed stream nutrient criteria.

Lacustrine groundwater discharge: Combined determination of volumes and spatial patterns

Summary The quantification of lacustrine groundwater discharge (LGD) in water and nutrient balances of lakes is challenging and thus often neglected. However, by carrying large nutrient loads, groundwater might play a key role in a lakes nutrient budget even if its contribution to the water balance is small. In the present study, we quantify the total annual LGD of a lake in northeastern Germany by the calculation of annual groundwater recharge in the subsurface catchment. Furthermore, spatial variability of LGD is expected to have significant influence on the nutrient balance due to heterogeneous nutrient concentrations. To assess its spatial variability, LGD is calculated for single sites based on vertical temperature profiles of the lake bed along the shoreline. The combination of the total LGD and the spatial LGD patterns allows calculating LGD volumes for single shoreline sub-sections. These calculations reveal that a large portion of the total LGD enters the lake within a relatively limited section of the shoreline. Scenarios including different phosphorus concentrations demonstrate the importance of both, quantity and patterns of LGD, when groundwater-borne phosphorus loads are calculated. At high, heterogeneous groundwater nutrient concentrations, it is crucial for lake nutrient budgets to reliably determine LGD patterns and volume.

Nutrient inputs to a Lagoon through submarine groundwater discharge: The case of Laoye Lagoon, Hainan, China

Submarine groundwater discharge (SGD) with inputs of nutrients in certain regions may play a significant role in controlling water quality in the coastal regions. In this paper, we have determined four naturally occurring radium isotope (223Ra, 224Ra, 226Ra and 228Ra) activities and nutrient concentrations in surface water, coastal groundwater and river water in the mixing zone of Laoye Lagoon to estimate the fluxes of SGD by several models. The activities of the four radium isotopes of ground water were considerably greater than those in surface water samples. Using a 224Ra/228Ra activity ratio (AR) model, we estimated the average lagoon water age to be 3.2days, which was comparable with the flushing time of 4.0days. Based on the excess radium isotopes and the water age of the lagoon, the estimated fluxes of SGD (in 106m3/d) ranged from 2.64 to 5.32 with an average of 4.11. Moreover, we used Si balance to evaluate the flux of SGD (4.8×106m3/d) which was close to the result calculated by radium. The SGD-derived nutrient fluxes (in mol/d) were DIN=1.7×105, PO43−=5.2×102, and SiO3=5.3×104. Furthermore, we applied the biogeochemical budget approach using SiO3 as a tracer to evaluate the impact of SGD. The differences between the results estimated by radium and SiO3 may indicate different pathways for the input of nutrients.

Submarine Groundwater Discharge-Derived Nutrient Loads to San Francisco Bay: Implications to Future Ecosystem Changes

Submarine groundwater discharge (SGD) was quantified at select sites in San Francisco Bay (SFB) from radium ( 223 Ra and 224 Ra) and radon ( 222 Rn) activities mea- sured in groundwater and surface water using simple mass balance box models. Based on these models, discharge rates in South and Central Bays were 0.3-7.4 m 3 day −1 m −1 .A l- though SGD fluxes at the two regions (Central and South Bays) of SFB were of the same order of magnitude, the dissolved inorganic nitrogen (DIN) species associated with SGD were different. In the South Bay, ammonium (NH4 + ) concentrations in groundwater were three-fold higher than in open bay waters, and NH4 + was the primary DIN form dis- charged by SGD. At the Central Bay site, the primary DIN form in groundwater and associated discharge was nitrate (NO3 − ). The stable isotope signatures (δ 15 NNO3 and δ 18 ONO3 )o f NO3 − in the South Bay groundwater and surface waters were both consistent with NO3 − derived from NH4 + that was isotopically enriched in 15 Nb y NH4 + volatilization. Based on the calculated SGD fluxes and groundwater nutrient concentrations, nutrient fluxes associated with SGD can ac- count for up to 16 % of DIN and 22 % of DIP in South and Central Bays. The form of DIN contributed to surface waters from SGD may impact the ratio of NO3 − to NH4 + available to phytoplankton with implications to bay productivity, phyto- plankton species distribution, and nutrient uptake rates. This assessment of nutrient delivery via groundwater discharge in SFB may provide vital information for future bay ecological wellbeing and sensitivity to future environmental stressors.

Impacts of invasive alien plants on water quality, with particular emphasis on South Africa

We review the current state of knowledge of quantified impacts of invasive alien plants on water quality, with a focus on South Africa. In South Africa, over 200 introduced plant species are regarded as invasive. Many of these species are particularly prominent in riparian ecosystems and their spread results in native species loss, increased biomass and fire intensity and consequent erosion, as well as decreased river flows. Research on the impact of invasive alien plants on water resources has historically focused on water quantity. However, although invasive alien plants also affect the quality of water, this aspect has not been well documented. Alien invasive plants increase evaporation rates, and reduce stream flow and dilution capacity. The biomass inputs of alien invasive plants, especially nitrogen fixers such as Acacia spp., alter nutrient cycles and can elevate nutrient concentrations in groundwater. Alien plant invasions alter the fire regimes in invaded areas by changing the size, distribution and plant chemistry of the biomass. More intense fires increase soil erosion and thereby decrease water quality. In contrast to riparian invasions, aquatic invasive plants have been more extensively studied in South Africa and their impacts on water quality have been relatively well monitored. Water quality in South Africa is rapidly deteriorating, and all factors that influence this deterioration need to be taken into account when formulating actions to address the problem. The changes in water quality brought about by alien plant invasions can exacerbate the already serious water quality problems.

Estimation of shallow groundwater discharge and nutrient load into a river

Pollution of rivers with excess nutrients due to groundwater discharge, storm water runoff, surface loading, and atmospheric deposition is an increasing environmental concern worldwide. While the storm water runoff and surface loading of nutrients into many rivers have been explored in great detailed, the groundwater discharge of nutrients into the rivers has not yet been thoroughly quantified. This study ascertained the shallow groundwater discharges and nutrient loads into the Lower St. Johns River (LSJR), FL, USA. The groundwater discharges were obtained using Darcy's law along with field measured hydrological parameters, whereas the groundwater nutrient loads were calculated based on the groundwater discharges and the field measured nutrient concentrations. The average rate of groundwater discharge per unit cross-section area over the four selected sites along the LSJR was about 1.2 × 10 −2 m 3 m −2 d −1. The average loads of groundwater nutrients into the adjacent LSJR were 10.6 and 5.6 mg m −2 d −1, respectively, for nitrate- and nitrite-nitrogen (NO x -N) and total phosphorus (TP). In general, seasonal variations of the groundwater levels were larger than the river stages, whereas site variations of groundwater nutrient concentrations were larger than seasonal variations of groundwater nutrient concentrations. Results from this study are useful for estimation of groundwater contamination and river eutrophication.

Quantifying Nutrients in Effluent from Uncovered, Intact Mature Bovine Carcass Compost Piles Subjected to Storm Events

Effluent pollutant concentrations and volumes were collected from uncovered, intact carcass, dairy cow mortality compost piles subjected to successive simulated 10.2 cm storm events after: (1) composting one cow in fresh sawdust only; (2) turning that pile, adding fresh amendment, adding a second cow, and composting it; and (3) turning the pile again, without an animal tissue addition. Phosphorus leaving an active mortality compost pile in runoff as produced by a 10.2 cm storm simulation ranged from 4.6 grams to 0.1 grams. Total COD in runoff ranged from 94 to 888 grams. Data indicated that the majority of nutrients in effluent leaving a pile from a 10.2 cm storm event infiltrate the soil surface. Total nitrogen mass load infiltrating the soil was estimated to range between 362 and 1778 grams under various management stages. With the exception of NO3, the nutrient concentrations in groundwater at 1.2 m soil profile depth were reduced by nine fold or more when compared to direct pile effluent, indicating that soil provided treatment of infiltrating pile effluent. No significant accumulation of soil nutrients below mortality compost piles occurred during the study. However, pile effluent nutrient characteristics indicate that soil nutrient accumulation may occur over time.

Groundwater nutrient concentrations during prairie reconstruction on an Iowa landscape

One anticipated benefit of ecosystem restoration is water quality improvement. This study evaluated NO 3-N and phosphorus in subsurface waters during prairie establishment following decades of row-crop agriculture. A prairie seeding in late 2003 became established in 2006. Wells and suction cup samplers were monitored for NO 3-N and phosphorus. Nitrate-N varied with time and landscape position. Non-detectable NO 3-N concentrations became modal along ephemeral drainageways in 2006, when average concentrations in uplands first became <10 mg NO 3-N L −1. This decline continued and upland groundwater averaged near 2 mg NO 3-N L −1 after 2007. The longer time lag in NO 3-N response in uplands was attributed to greater quantities of leachable N in upland subsoils. Spatial differences in vadose-zone travel times were less important, considering water table dynamics. Phosphorus showed a contrasting landscape pattern, without any obvious temporal trend. Phosphorus was greatest along and near ephemeral drainageways. Sediment accumulation from upland agricultural erosion provided a source of P along drainageways, where shallow, reductive groundwater increased P solubility. Phosphorus exceeded eutrophication risk thresholds in these lower areas, where saturation-excess runoff could readily transport P to surface waters. Legacy impacts of past agricultural erosion and sedimentation may include soluble phosphorus in shallow groundwater, at sites prone to saturation-excess runoff.

Human impacts on large benthic foraminifers near a densely populated area of Majuro Atoll, Marshall Islands

Human impacts on sand-producing, large benthic foraminifers were investigated on ocean reef flats at the northeast Majuro Atoll, Marshall Islands, along a human population gradient. The densities of dominant foraminifers Calcarina and Amphistegina declined with distance from densely populated islands. Macrophyte composition on ocean reef flats differed between locations near sparsely or densely populated islands. Nutrient concentrations in reef-flat seawater and groundwater were high near or on densely populated islands. δ15N values in macroalgal tissues indicated that macroalgae in nearshore lagoons assimilate wastewater-derived nitrogen, whereas those on nearshore ocean reef flats assimilate nitrogen from other sources. These results suggest that increases in the human population result in high nutrient loading in groundwater and possibly into nearshore waters. High nutrient inputs into ambient seawater may have both direct and indirect negative effects on sand-producing foraminifers through habitat changes and/or the collapse of algal symbiosis.

Nutrient inputs to the coastal ocean from submarine groundwater discharge in a groundwater‐dominated system: Relation to land use (Kona coast, Hawaii, U.S.A.)

We evaluated the magnitude and composition (in terms of salinity, 223Ra and 224Ra activity, and nutrient concentrations) of submarine groundwater discharge (SGD) fluxes at 11 sites on the Kona coast of Hawaii. Discharging groundwater was typically brackish to saline and had high Ra activity relative to ocean water and fresher, inland groundwater. Brackish SGD fluxes, estimated using a mass‐balance approach based on excess coastal ocean 224Ra activity, ranged from 3 to 1300 L m−1 of coastline min−1. Fluxes of the freshwater component of SGD, calculated based on salinity, ranged from 2 to 310 L m−1 min−1. Nutrient fluxes into coastal waters from SGD varied by up to three orders of magnitude among sites. Nitrate + nitrite (N + N), phosphate, and silica concentrations showed strong, inverse linear correlations with salinity in coastal seawater and groundwater. These correlations were consistent with previous work that documented conservative mixing between fresh, high‐nutrient groundwater and saline, low‐nutrient seawater at a few coastal ocean sites. We extend this conservative relationship to more coastal ocean sites and to groundwater in the coastal aquifer. N + N concentrations in the fresh component of discharging groundwater were higher at sites near golf courses and those with a greater percentage of bare land within a 5‐km radius, and silica concentrations in the fresh component of discharging groundwater were higher at sites with more bare land and lower population densities. However, neither urbanization nor agriculture was significantly correlated with groundwater nutrient concentrations on this relatively undeveloped coast.

Nutrient Variation in an Urban Lake Chain and its Consequences for Phytoplankton Production

In the Central Arizona-Phoenix (CAP) ecosystem, managers divert mixed stream water and groundwater to maintain an artificial lake chain in Indian Bend Wash (IBW), a historically flashy, ephemeral, desert stream. Nutrient concentrations in the CAP ecosystem's groundwater, stream water, and floodwater differ: stream water has low concentrations of both inorganic N and P, while groundwater is low in inorganic P but rich in nitrate (NO(3)(-)). Consequently, groundwater contribution drives inorganic N concentrations in the lake chain. In contrast, floodwater typically has high P concentrations while remaining low in N. Thus we expected N and P concentrations in IBW lakes to vary with the mix of water flowing through them. Elevated NO(3)(-) and low inorganic P concentrations were predicted when groundwater pumping was pronounced and this prediction was supported. We hypothesized that these predictable changes in water chemistry would affect nutrient limitation of phytoplankton. Laboratory nutrient-addition bioassays demonstrated that phytoplankton growth was P-limited throughout the summer of 2003 when N/P was high. However, after a late-season flood drove N/P below 31:1, the expected threshold between N and P limitation, N limitation was observed. Our results indicate that effects of floods, the preeminent historic drivers of Sonoran Desert stream biogeochemistry, are mitigated in urban ecosystems by decisions about which spigots to turn. Consequently, nutrient limitation of urban streams is driven as much by management decisions as by natural hydrologic variation.

Long-term performance of a representative integrated constructed wetland treating farmyard runoff

The integrated constructed wetland (ICW) system studied in this research paper was constructed as part of a series of 15 wetland systems to improve the water quality of an entire catchment area (Annestown Stream watershed, Ireland) dominated by farming activities. The studied ICW comprised four cells and was used for the treatment of farmyard dirty water from a dairy farm near Dunhill (Ireland). The performance of this system was evaluated through physical, chemical and microbiological parameters collected for 7 years. The removal efficiencies were relatively good if compared to the international literature: biochemical oxygen demand (97.6%), chemical oxygen demand (94.9%), suspended solids (93.7%), ammonia-nitrogen (99%), nitrate-nitrogen (74%) and molybdate reactive phosphorus (91.8%). A molecular microbiological analysis of sediment samples collected from the site indicated that the number of denitrifying bacteria detected in the ICW system was higher than the number of ammonia-oxidizing bacteria. The monitored nutrient concentrations in groundwater and surface waters indicated that this ICW system did not pollute the receiving waters. The results showed that ICW are likely to be efficient in removing nutrients from farmyard runoff rich in nitrogen and phosphorus.

Tidal pumping drives nutrient and dissolved organic matter dynamics in a Gulf of Mexico subterranean estuary

We hypothesize that nutrient cycling in a Gulf of Mexico subterranean estuary (STE) is fueled by oxygen and labile organic matter supplied by tidal pumping of seawater into the coastal aquifer. We estimate nutrient production rates using the standard estuarine model and a non-steady-state box model, separate nutrient fluxes associated with fresh and saline submarine groundwater discharge (SGD), and estimate offshore fluxes from radium isotope distributions. The results indicate a large variability in nutrient concentrations over tidal and seasonal time scales. At high tide, nutrient concentrations in shallow beach groundwater were low as a result of dilution caused by seawater recirculation. During ebb tide, the concentrations increased until they reached a maximum just before the next high tide. The dominant form of nitrogen was dissolved organic nitrogen (DON) in freshwater, nitrate in brackish waters, and ammonium in saline waters. Dissolved organic carbon (DOC) production was two-fold higher in the summer than in the winter, while nitrate and DON production were one order of magnitude higher. Oxic remineralization and denitrification most likely explain these patterns. Even though fresh SGD accounted for only ∼5% of total volumetric additions, it was an important pathway of nutrients as a result of biogeochemical inputs in the mixing zone. Fresh SGD transported ∼25% of DOC and ∼50% of total dissolved nitrogen inputs into the coastal ocean, with the remainder associated with a one-dimensional vertical seawater exchange process. While SGD volumetric inputs are similar seasonally, changes in the biogeochemical conditions of this coastal plain STE led to higher summertime SGD nutrient fluxes (40% higher for DOC and 60% higher for nitrogen in the summer compared to the winter). We suggest that coastal primary production and nutrient dynamics in the STE are linked.