Phosphorus Fluxes Research Articles

Effects of nutrient-rich submarine groundwater discharge on marine aquaculture: A case in Lianjiang, East China Sea

Submarine groundwater discharge (SGD) and associated nutrient have long been received insufficient attention in the aquaculture areas of Lianjiang, East China Sea. In this study, we used 224Ra mass balance model to evaluate the importance of SGD in the aquaculture areas of Lianjiang in different seasons. The results showed that SGD fluxes were 0.14 ± 0.070 m3 m−2 d−1 in July and 0.077 ± 0.040 m3 m−2 d−1 in October 2019, which corresponded to approximately 22% and 32% of the river discharge, respectively. Nevertheless, the dissolved inorganic nitrogen (DIN) and phosphorus (DIP) fluxes contributed by SGD over total nutrient inputs were approximately 58% and 73%, respectively in July, 11% and 33%, respectively in October 2019. The ratio of DIN to DIP in seawater was slightly higher than that derived from SGD in July and significantly lower than that derived from the river and SGD in October, which was prone to profound modulated by shellfish (e.g., clam Ruditapes philippinarum and Sinonovacula constricta) and nori (e.g., Pyropia haitanensis) that selectively acquire nitrogen and phosphorous, suggesting that SGD could affect the nutrient structure and aquaculture activities in Lianjiang. Moreover, the new primary production via SGD yielded (2.47 ± 1.32) × 103 mg C m−2 d−1 in July and (3.52 ± 1.76) × 102 mg C m−2 d−1 in October 2019, which were approximately 8–25% and 10–31% of the production in the entire study area. These meaningful discoveries indicated that SGD and associated nutrient are the predominant regulator of nutrient and aquaculture structure under significant seasonal differences.

Long term simulations of macronutrients (C, N and P) in UK freshwaters

Over the last two centuries, the landscape of many industrialised nations has been transformed by the spread and intensification of agriculture, by atmospheric pollution, by human waste (rising in line with population growth), and now by changes in the climate. The research presented here aims to understand and quantify how these long-term changes have impacted UK freshwaters and the flux of macronutrients to the sea. The Long Term Large Scale (LTLS) Freshwater Model presented here used readily-available driving data (climate, land-use, nutrient inputs, catchment topography) to understand and quantify how changes in the UK's macronutrient histories have impacted on freshwater stores and fluxes. Model-reconstructed sources and fluxes of carbon, nitrogen and phosphorus (C, N and P) from 1800 to 2010 indicate that the rapid increase in the use of agricultural fertilisers after the second world war, and the rising human population, led to a rapid rise in N & P fluxes to rivers. During this period, the modelling shows that the dominant source of N in rivers changed from improved grassland to arable, the dissolved N export to rivers quadrupled, and P from human waste increased by ~600%, despite waste water treatment. The simulations also indicate a net storage of nitrates in groundwater between the 1940s and 1990s, and a net release to coastal waters post-1990; but groundwater retention and later release of C&P are less significant. Overall, modelling indicates that >75% of C, N and P entering freshwaters goes directly to the coastal waters, with 15–20% of C & N removed in river processes. These results constitute the first process-based integrated modelling assessment of freshwater macronutrient change at a national scale. The LTLS approach provides a methodology to develop fully-coupled global models of terrestrial, freshwater, atmospheric and marine processes that can take account of changes in land-management and climate.

Nitrogen and phosphorus flux in wastewater from three productive stages in a hyperintensive tilapia culture

Abstract In this research, effect of productive stages in nitrogen and phosphorus excretion in wastewater from hyperintensive tilapia (Oreochromis niloticus) culture was evaluated. Fish were cultivated considering three development stages (fingerling of 1.79 g, juvenile of 36.13 g, and adult of 72.96 g). Nitrite, nitrate, ammonium, and phosphorus concentration were determined in order to know the amount of nutrients excreted per productive stage of the fish at a high stocking density. Biometric data were recorded during the experiment with the purpose of determining the growth behavior of fish, as well as the measurement of the aerobic metabolism. Results showed that survival, growth, and health of fish are not affected by hyperdensity of culture; as well, combined catabolism of proteins and lipids was presented as substrates for energy with value for O:N ratio ranging between 20 and 60. In addition, higher concentration in excretion of nitrogen compounds and phosphorus per gram of fish was recorded in wastewater from a hyperintensive culture in fingerlings than in juveniles and adults. These results suggest the use of this wastewater in the early stages of fish growth, aiming to enhance sustainable systems with maximum use of the resources, such as aquaponics systems.

Bibliometric Analysis of Research on the Water and Sediment Environment in the Middle  Lower Changjiang River Basin

To elucidate research progress, hotspots, and trends regarding the water and sediment environment in the Changjiang River Basin, a bibliometric analysis of research published on the water and sediment in the middle-lower reaches of the Changjiang River, from 1991 to 2020, was conducted, according to the Web of Science Core database. With regard to the number of papers, distribution of research institutions, tracking of research hotspots, related disciplines, highly cited literature, etc., a comprehensive statistical analysis was conducted to investigate the research characteristics, research status, and development trends of the water & sediment environment in the middle-lower section of the Changjiang River. Combined with the latest trends in water and sediment environment research, important future research directions were investigated. The results indicated that, among the literature, the Chinese Academy of Sciences(CAS) was the largest contributor to study on the water and sediment environment of the Changjiang River, followed by universities along the Changjiang River. Chinese scientific research institutes paid the most attention to changes in the water and sediment environment of the Changjiang River and cooperated on an international level with other countries. From the perspective of discipline distribution, the number of papers on ecological environment was the highest, followed by that on geological environment, water resources, engineering, and oceanography. The amount of research conducted on water and sediment transport, riverbed change, water pollution, and other issues was relatively high. According to the highly cited literature, water contamination and sediment were the main concerns. Combined with high-frequency keywords — and by consulting the relevant literature — this paper presented the hot spots of the water and sediment environment in the middle-lower reaches of the Changjiang River. It is determined that the implementation of water conservancy projects in the upper reaches of the Changjiang River has changed the path, release mechanism, and role of phosphorus, as well as the ecological environment of the Changjiang River Basin and its estuary. Change of phosphorus flux and its effect on environment are one of the most important directions for future water and sediment environment research.

A dynamic flux model for analyses of phosphorus exchange between overlying water and sedimentary deposits of a reservoir in the cold area of north China

In this study, to clarify the quantitative relationship between the exchange flux of total phosphorus and water environment factors at the sediment-overlying water interface in reservoirs, and to reveal that the seasonal variation of total phosphorus exchange flux at the sediment-overlying water interface changes when the water environmental factors change in reservoirs located in cold regions, water environment factors including pH, DO, temperature, and others were analyzed. Specifically, in 2018, sediment samples of the Dahekou Reservoir from XilinGol League were collected, and via indoor orthogonal simulation experiments, a mathematical model of the total phosphorus exchange flux at the sediment–overlying water interface and environmental factors was established, i.e., R = 0.791 + 0.018[T] + 0.048[pH] - 0.180[DO] + 0.004[K]. This model was then combined with the input load of total phosphorus in the Luanhe and Tuligen rivers in the upper reaches of the reservoir in order to assess the contribution rate of the total phosphorus release load to the total phosphorus input from the reservoir. The results showed that the total phosphorus release pollutant load in the sediments of the Dahekou Reservoir was 0.297 t/a in 2018. The flux of total phosphorus at the sediment-overlying water interface showed seasonal changes: summer > spring > autumn > winter. The release load of total phosphorus in sediments in spring was 0.014–0.042 t/month, and the contribution rate to the total phosphorus input from the reservoir was 16.67%–26.44%. The contribution rate of total phosphorus release in summer from the sediments to the overlying water was 19.71%–33.56%. Although this was the highest value of the entire year, due to the role of water temperature stratification in the summer, its actual contribution to the total phosphorus input pollution in reservoirs may not be significant. The total phosphorus released from the sediments in autumn was 0.067–0.397 t/month, and the contribution rate to total phosphorus input pollution in the reservoir decreased to 5.28%–11.19%. In winter, the water temperature decreased, and the concentration of dissolved oxygen increased. These changes to the water environment increased the phosphorus release from water to sediment, with the exchange flux of total phosphorus between sediment and water changing from −0.004 to −0.011 t/month.

Characteristics of Soil Nitrogen and Phosphorus Losses Under Different Land-use Schemes in the Shipanqiu Watershed

In order to understand the characteristics of soil nitrogen and phosphorus loss under different land use patterns in the small watershed of the Three Gorges Reservoir area and provide a scientific basis for the prevention and control of agricultural non-point source pollution, a field test method was used to study the paddy fields and drought in the small Shipanqiu Watershed in the Three Gorges Reservoir area. The characteristics of different runoff concentrations and the fluxes of nitrogen and phosphorus in surface runoff under the five land use schemes of paddy filed, slope land, woodlands, citrus orchards, and vegetable land. The results show that the annual total nitrogen loss followed the order of paddy field[17.73 kg·(hm2·a)-1] > citrus orchards[4.86 kg·(hm2·a)-1] > dry slope land[4.33 kg·(hm2·a)-1] > vegetable field[4.00 kg·(hm2·a)-1] > woodland[2.41 kg·(hm2·a)-1]. The annual total phosphorous loss followed the order of vegetable fields[4.97 kg·(hm2·a)-1] > Citrus orchards[1.87 kg·(hm2·a)-1] > paddy fields[0.93 kg·(hm2·a)-1] > woodlands[0.27 kg·(hm2·a)-1] > dry slope land[0.19 kg·(hm2·a)-1]. The nitrogen and phosphorus losses under the five land use methods were mainly concentrated from April to May with frequent rainfall events, accounting for 53.80%-96.52% and 56.03%-87.78% of the total annual nitrogen and phosphorus losses. Nitrogen loss was mainly in the form of nitrate nitrogen (16.16%-52.70%), and the total nitrogen loss flux and runoff showed a significant positive correlation (R2=0.9826). Particulate phosphorus was the main form of phosphorus loss in vegetable fields (83.30%), but in other land use schemes it is not significant. There were significant differences in the loss of different forms of nitrogen and phosphorus under the different land use schemes. Among them, measures should be taken in vegetable fields to deal with the problem of particulate phosphorus loss under conditions of heavy rainfall. Fertilization should be avoided in paddy fields during periods of concentrated rainfall. Scientific fertilization and reasonable land use configurations are important ways to control agricultural non-point source pollution in small watersheds.

Water Exchanges and Phosphorus Flux between a Reservoir and Eutrophic Littoral Zone

HighlightsConvective currents led to hydraulic flux and transport of P between bottom and surface waters of the littoral zone.Hydraulic flux was primarily into the bottom of the cove and out of the cove along the surface.Eutrophic littoral areas are a significant source of P to the photic zone of reservoirs, supporting algal growth.Abstract. Eutrophication of surface waters is defined by excessive algal growth, with consequences for drinking water treatment. The sources of phosphorus (P) in southern U.S. reservoirs that fuel peak algal productivity in late summer are still not fully understood. One potential source is reservoir littoral zones, which have been described as the most productive zone of a waterbody. A shallow cove named Granny Hollow in Beaver Lake, northwest Arkansas, was selected as an isolated and semi-controlled location to measure and model sources of P and its transport in a littoral area for the month of July 2018. Hydraulic and P fluxes between the reservoir and littoral area were quantified through field measurements and a 3D lake model. In quantifying hydraulic flux for the month of July, the model indicated that water tended to move into the cove along the bottom and out along the top, with a net hydraulic flux out of the cove of -723,000 m3. Peak surface velocity in the cove averaged 2.09 cm s-1 for the month of July, while peak bottom velocity was 1.29 cm s-1. Diurnally, water movement switched directions, moving out of the cove along the surface during differential heating and into the cove along the surface during differential cooling due to thermoconvective flow. During differential heating, the water velocity and hydraulic flux to the main reservoir channel along the surface of the cove were greater than the velocity and flux in the opposite direction during differential cooling. The sources of P within the cove during July included P released from bottom sediments within the cove and littoral zone and transport of P from the reservoir channel to the cove. Transport of P from the main reservoir into the cove was a result of thermoconvective flow. During differential heating, bottom waters from the main reservoir channel were transported to the surface within the littoral zone by thermoconvective currents flowing upslope from deeper to shallower waters. This resulted in P exchange between the reservoir and littoral area and is significant because it represents movement of P from the bottom of the reservoir upward into the photic zone, where it can be used for algal productivity. During July 2018, it was estimated that 13.3 kg of P were transported from the bottom of the cove to the surface by convective currents and subsequently out of the cove. This study shows that eutrophic coves represent a significant source of P to the reservoir and more importantly to the photic zone, supporting algal growth. Keywords: 3D reservoir model, Eutrophication, Internal loading, Thermoconvective flow.

Concentration and Diffusion of Nutrients in the Interpore–Bottom Water System of the Ob River Estuary

On cruise 76 in 2019, the R/V Akademik Mstislav Keldysh completed the Gulf of Ob–Kara Sea slope transect. Samples of bottom water and two sediment layers 1 cm thick were obtained with a multicorer. The silicon, mineral and total phosphorus, and organic nitrogen concentrations were measured in them. The magnitude of fluxes of these nutrients at the water–bottom boundary along the transect was calculated; they are all positive, i.e., directed from sediment to water. Comparison of silicon and phosphates fluxes obtained in the transect in 2019 with fluxes measured on a similar transect in 2007 showed good agreement. Silicon fluxes along the transect vary little (less than two times), including the frontal river–sea mixing zone. Mineral phosphorus fluxes have two maxima: in pure river waters and on the slope of the Kara Sea. In the area of the lens of freshened waters, phosphorus fluxes can have an alternating character, depending on season, the state of production, and destructive processes. A method is proposed for comparing fluxes of different nutrients in order to establish the nature of their variability along the transect and to identify measurement errors.

Sediment phosphorus fractionation and flux in a tropical shallow lake

Abstract: Aim The aim of the present study is to evaluate the potential phosphorus (P) release from the sediment to the water column of a tropical shallow lake in the northeast of Brazil, based on the sediment P fractions and on the flux of P between water and sediment. Methods We used a sequential extraction method to analyse the different P fractions of the sediment of Lake Extremoz. We also carried out a 40-day microcosm experiment to analyse the flux of P between water and sediment. We did so by flooding 200g of sediment from the lake with 800 mL of 1.2 µm filtered lake water in 1 L beakers. Every 5 days we analysed: soluble reactive phosphorus (SRP), total phosphorus (TP), organic phosphorus (Org-P), dissolved oxygen (DO), temperature, and pH of the water. Results The largest fraction of P in the sediment of Lake Extremoz is Refractory-P, which is non-mobile. The main mobile fraction of this lake’s sediment is composed of P bound to Fe and Mn oxides (BD-P) which is redox sensitive. During the P flux experiment, the water was always oxic and with nearly neutral pH, however the temperature increased by almost 4 °C due to the increase of the temperature of the air. SRP, TP and Org-P concentrations in the water had a general decrease in the first 20 days. But, on the second half of the experiment, those concentrations increased and the fluxes of P from sediment to water, mainly Org-P, were positive. Even with this increase in concentrations, indicating a period of P release, overall fluxes were negative. Conclusions The main mobile fraction of the sediment is redox sensitive, therefore it has the potential to be released in case of oxygen depletion. Under current conditions, most of the P released by the sediment is in organic forms, indicating that, in the presence of oxygen, the balance of P between water and sediment is controlled by the effects of organisms on P as well as temperature.

Processes controlling the flux of legacy phosphorus to surface waters at the farm scale

Phosphorus (P) leaching from agriculture is a major driver of water eutrophication in downstream rivers and lakes. In drained lowland areas with intensive agriculture, a reduction in the fertilizer applications may be insufficient to improve the water quality in the short term as the P accumulated in the soil during decades of high fertilization may continue leaching for many years. A complementary approach to reduce P exports from agriculture is to implement edge-of-field mitigation measures at the farm scale. The selection of effective measures requires a detailed insight into the chemical and hydrological transport mechanisms. Here, we determined the main P sources, processes, and transport routes at the farm scale to support the selection of appropriate mitigation measures. We quantified the legacy P, the different P pools stored in the upper soil, and related it to the yearly P export downstream. To do this, we combined high-resolution monitoring data from the soil, groundwater, surface water, and ditch sediments. The legacy P in the topsoil was high, about 2500 kg ha−1. The predominant subsurface flow and the subsoils’ P sorption capacity retained the P mobilized from the topsoil and explained the relative moderate flux of P to surface waters (0.04 kg ha−1 during the 2018–2019 drainage season). The dissolved P entering the drainage ditch via groundwater discharge was bound to iron-containing particles formed due to the oxidation of dissolved ferrous iron. Once leached from the soil to the drainage ditch, resuspension of P-rich sediment particles during flow peaks were the most important P transport mechanism (78%). Therefore, we expect that hydraulic constructions that reduce flow velocities and promote sedimentation of P-containing particles could reduce the export of P further downstream.

Land‐use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments

AbstractAgricultural, forestry‐impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry‐impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (−15 μg totN L−1 year−1) and natural (−0.4 μg NO3‐N L−1 year−1) catchments, but individual sites displayed few long‐term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry‐impacted sites had a significant decline in totP (−0.1 μg P L−1 year−1). A small but significant increase in totP fluxes (+0.4 kg P km−2 year−1) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large‐scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs.

Spatio-Temporal Dynamics of Riverine Nitrogen and Phosphorus at Different Catchment Scales in Huixian Karst Wetland, Southwest China

Spatio-temporal dynamics of riverine nitrogen (N) and phosphorus (P) in karst regions are closely linked to hydrological conditions, human activities and karst features in upstream catchments. From October 2017 to September 2019, we undertook 22 sampling campaigns in 11 nested catchments ranging from 21.00 to 373.37 km2 in Huixian karst wetland to quantify forms, concentrations, and fluxes of riverine total nitrogen (TN) and total phosphorus (TP), and to identify spatial and temporal variations of nutrients transfer from upstream to downstream, tributaries (Mudong River and Huixian River) to the main stem (Xiangsi River) in the dry and wet seasons. Considering the hydrological conditions, human activities and karst features within upstream catchments, the following three spatial and temporal variations of riverine nutrients were found over the monitoring period: (1) the dynamics of riverine nitrogen and phosphorus varied seasonally with hydrological conditions; (2) the spatial disparities of riverine nitrogen and phosphorus were induced by different human activities within catchment scales; (3) the dynamics of riverine nitrogen and phosphorus varied similarly at spatial scale restricted by karst features. The findings from this study may improve our understanding of the influence of hydrological conditions, human activities and karst features on nitrogen and phosphorus variations in river waters at different spatial and temporal scales in the Huixian karst wetland basin, and will help managers to protect and restore river water environments in karst basin from a catchment-scale perspective.

Identifying sources of phosphorus in precipitation using phosphate oxygen isotope in a human and monsoon Co-affected embayment

The phosphorus in precipitation provides a significant fraction of the bioavailable phosphorus to fresh and marine waters. To identify the possible sources and interpret the atmospheric deposition processes of phosphorus, we measured the phosphate oxygen isotopes (δ18OP) in the precipitation monthly from October 2015 to March 2017 in Daya Bay, South China Sea. The isotopic results show that the δ18OP values in the dry season (+19.60‰ to +25.80‰, +23.10‰ average) were significantly higher than those in the wet season (+12.52‰ to +20.11‰, +16.73‰ average), indicating a variable contribution from different phosphorus sources to the precipitation between seasons. The δ18OP value was primarily influenced by the phosphorus concentrations, rainfall, and air temperature. The exchange of phosphate molecules among phosphorus pools caused isotope dilution (wet season) or enrichment effects (dry season) during the seasonal shifts. The δ18OP value of the precipitation and the local end-members indicate that coal combustion (39% ± 16%), biomass burning (22% ± 18%), and soil (17% ± 13%) sources dominate in the dry season, whereas marine sources (28% ± 19%) and coal combustion (24% ± 12%) account for the highest proportion in the wet season using a MixSIAR model. The atmospheric wet deposition flux of phosphorus in Daya Bay was 379.0 μmol m−2·yr−1. The wet deposition of phosphorus exhibits a significant seasonal trend with higher deposition fluxes in the wet season than in the dry season as a result of higher rainfall and source shifts (local sources to marine source) between seasons.

Large pools and fluxes of carbon, calcium and phosphorus in dense charophyte stands in ponds

Bicarbonate and calcium set bounds on photosynthesis and degradation processes in calcareous freshwaters. Charophytic algae use bicarbonate in photosynthesis, and direct variable proportions to assimilate organic carbon and to precipitate calcium carbonate on their surfaces. To evaluate pools of organic carbon (Corg), carbonate carbon (Ccarbonate), and phosphorus (P) in dense charophyte vegetation, we studied apical and basal tissue and carbonate surface precipitates, as well as underlying sediments in ten calcareous ponds. We also quantified the release of calcium, bicarbonate and phosphate from charophyte shoots in dark experiments. We found that the Corg:Ccarbonate quotient in charophyte stands averaged 1.19 during spring and summer. The Corg:Ccarbonate quotient in the sediments formed by dead charophytes averaged 0.97 in accordance with some respiratory CO2 release without carbonate dissolution to bicarbonate. The molar quotient of carbon to calcium was close to 2.0 in sediment and pond water. In dark incubations, shoots subjected to calcium carbonate dissolution released bicarbonate and calcium with a molar quotient of 2:1; lowered pH (7.0–8.0) increased the release. Thus, the carbonate surface crust on living charophytes was not inert, as hitherto anticipated. Phosphate dark release occurred from basal shoots only, was unrelated to pH, and may have derived from organic decomposition, rather than from carbonate dissolution. Extensive phosphorus pools were associated with the charophyte stands (200–600 mg m−2) and had about 2/3 incorporated in alga tissue and 1/3 in carbonate crust. Overall, the biogeochemistry of carbon, calcium and phosphorus are closely linked in calcareous charophyte ponds. Carbonate dissolution from charophyte crusts at night and continuously from sediment might balance extensive carbonate precipitation during daytime photosynthesis. The substantial P-pool in charophyte stands may not derive from P-deprived water, but from P-rich sediment. Charophyte photosynthesis may still contribute to nutrient-poor conditions by forming carbonate-rich sediment of high P-binding capacity.

Potential of aquatic weeds to improve water quality in natural waterways of the Zambezi catchment

One prominent effect of nutrient pollution of surface waters is the mass invasion of floating plants, which can clog waterways, disrupting human use of aquatic systems. These plants are widely vilified and motivate expensive control campaigns, but their presence may be providing a poorly recognized function in the cycling of excess nutrients. The capacity for floating plants to absorb nutrients from surface water has been understood for decades, primarily from their use in constructed wetlands for wastewater treatment. Yet, in natural settings, there has not been to date any effort to quantify whether floating plant invasions represent important pools or fluxes of nutrients relative to those of the river catchments in which they occur. We found that seasonal hydrologic cycles in the Zambezi trap and flush floating plants from river choke points, such as dams and river confluences, on an annual basis. Peak plant biomass at such choke points constitutes a proxy for estimating annual plant-bound nutrient loads. We assessed the significance of floating vegetation as nutrient sinks by comparing annual plant-bound nutrient loading to conventional river nutrient loading (dissolved and particulate) for four tributaries of the Zambezi River in Zambia. We found that the relative importance of floating vegetation was greatest in the more urbanized catchments, such as the Maramba River draining the city of Livingstone, representing approximately 30% and 9% of annual digestible phosphorus and nitrogen flux respectively. We also found plant-bound phosphorus to be important in the Kafue River (19%), draining the industrial town of Kafue and extensive sugarcane plantations. These results demonstrate the great potential of floating plants to take up excess nutrients from natural river systems. Given the importance of hydrology in the life cycle of floating vegetation, controlled dam discharges may have an important role in managing them and their water quality treatment functions.

Human-driven spatiotemporal distribution of phosphorus flux in the environment of a mega river basin

Large river basins transport considerable nutrients to the ocean every year. However, phosphorus (P) generated by human activities not only threatens aquatic ecosystem health in the river basin, but also has a negative effect on the estuary water environment. To better understand the environmental effects of anthropogenic P in a mega basin, we examined its inputs and distribution characteristics, and analyzed the factors driving it in the Yangtze River Basin (YRB) and sub-catchments. Anthropogenic P flux in the sub-catchments gradually increased from upper to lower reaches, and hotspots were primarily concentrated in traditional agricultural areas such as the Sichuan Basin and the Middle-Lower Yangtze plains. Agricultural sources were the main anthropogenic P inputs, of which fertilizer P was the leading contributor and driver of P changes, but livestock manure also accounted for a high proportion. Presently, anthropogenic P inputs in the YRB are considerably higher than in other parts of the world. Although long-distance transportation allows some P from the entire basin to be deposited in freshwater, a large amount of P still reaches the estuary and has a negative effect on water quality, outweighing the influence of local coastal inputs. To maintain the ecological health of the river basin and estuary, it will be necessary to further improve P utilization efficiency and encourage greater cooperation between different regions in the river basin.

Stream Restoration for Legacy Sediments at Gramies Run, Maryland: Early Lessons from Implementation, Water Quality Monitoring, and Soil Health

While stream restorations are increasingly being adopted to mitigate sediment and nutrient inputs and to meet water quality regulatory targets, less information is available on the drivers behind the design, implementation, effectiveness, and cost of restorations. We address these issues for a $4.2 million stream restoration for legacy sediments implemented for a rural Piedmont stream in Maryland, USA. A total of 1668 m of stream was restored in three phases, which included the partial removal of legacy sediments, the grading of streambanks, floodplain creation, channel reshaping with meanders and pool-riffle forms, the raising of the stream bed, and the planting of riparian vegetation. The sediment, nitrogen, and phosphorus concentrations and fluxes were monitored before- and during the restoration phases. The sites selected for restoration had legacy sediments vulnerable to erosion and were on state-owned land. The restoration design was based on the need to maintain mature riparian trees and preserve existing sensitive wetland habitats. Water quality monitoring indicated that the sediment and nutrient fluxes increased during the restoration phase and were attributed to disturbance associated with construction activities and increased runoff. We also recommend that soil health needs to be included as an integral component to enhance the effectiveness and resilience of stream restorations.

Using plug-flow column reactor data to constrain calcic mineral weathering rates from watershed mass-balance methods: Lithogenic apatite dissolution and phosphorus fluxes into the Loch Vale Watershed ecosystem, Colorado, USA

Sources of phosphorus (P5+) to ecosystems can be very difficult to identify and quantify due to P5+ being monoisotopic. Previous field-based, watershed mass-balance calculations of the lithogenic P5+ flux in the alpine/subalpine Loch Vale watershed (LVW) of Colorado, USA suggested that weathering was controlled by one of three acid-weathering scenarios: (1) All minerals experience only carbonic acid weathering; (2) all minerals experience both carbonic acid and sulfuric acid weathering; and (3) only silicate minerals experience sulfuric acid weathering. We used a plug-flow column reactor to provide additional constraints that strongly indicate scenario (1) (carbonic acid-only weathering) explains the stream chemistry at the LVW outlet (1984–2008 period of sampling). Therefore, sulfuric acid generated by pyrite oxidation in the LVW is not significantly involved in chemical weathering reactions. In the column reactor, calcite dissolution by carbonic acid seemed to suppress apatite dissolution with the likelihood of this suppression confirmed by thermodynamic modeling and comparison to kinetic data. The comparability between column reactor and watershed-scale data likely reflects the LVW landscape being dominated by relatively high rates of mechanical weathering. The lithogenic P5+ flux from the LVW is solely attributable to apatite (Ca5(PO4)3(OH,F,Cl)) dissolution and is ~47 mol ha−1 yr−1, ~18 times greater than the modeled global average. The relatively high solubility of apatite in the Loch Vale watershed likely results from substantial quantities of radionuclides hosted as substituted elements in the crystal lattice, which may cause loss of crystallinity due to self-irradiation. Aeolian inputs to landscapes may supplement any P5+ from primary phosphate mineral dissolution. These natural sources of P5+ are likely contributing to the increases in algal biomass observed today.

Variation of net anthropogenic phosphorus inputs (NAPI) and riverine phosphorus fluxes in seven major river basins in China

The riverine phosphorus (P) import resulting from human activities is always a worldwide concern for environmental management due to the effect of eutrophication. In this study, we made modification of the NAPI method to make the results closer to the actual situation. We collected the data of seven major outflow rivers in China to have a comprehensive understanding of P export and P inputs and build the quantitative relationship between them. We estimated the net anthropogenic phosphorus inputs (NAPI), including fertilizer P (Pfert), net food and feed import P and non-food P using by human (Pim+nf), in seven major river basins in China and the corresponding riverine total phosphorus (TP) fluxes. The relationship between NAPI and riverine TP flux was also explored. NAPI in seven river basins presented an obvious uneven distribution. Huaihe River basin showed the highest NAPI of 4005.09 kg P km−2 yr−1 due to its highest intensities of human-activities, and the lowest NAPI was observed in Songhua River basin as 334.36 kg P km−2 yr−1. Pim+nf occupied a larger proportion of NAPI in the Pearl River and Liaohe River basins (> 65%), while Pfert contributed more to NAPI in the other basins (nearly 60%) with an exception of the Yangtze River basin (where Pim+nf and Pfert approximately contributed the same). Different contributions of NAPI components were mainly attributed to the different land uses. The total TP flux of all the seven rivers was 117.10 × 103 t P yr−1, with the highest flux in the Yangtze River (77.42 × 103 t P yr−1), contributed 72.88% to the total TP fluxes in China. Change in riverine TP flux could be well described by NAPI, river discharge, and percentage of lake area in the basin and this provided an effective way to predict TP fluxes in rivers.

The transborder flux of phosphorus in the Lancang-Mekong River Basin: Magnitude, patterns and impacts from the cascade hydropower dams in China

Nutrients are critical to the development of plant and animal life in the river ecological system. In recent years, more attentions have arisen on the impact of building hydropower dams to transborder nutrient flux in the Lancang-Mekong River Basin (LMRB). In this paper, phosphorus was taken as an example, which is considered as one of the most significant factors to limit biological activities in the river. The Soil and Water Assessment Tool (SWAT) was used to access the multisource loading pattern of Total Phosphorus (TP) under no-dam scenario, and various types of dam construction scenarios analyses were performed to investigate potential changes in the transborder TP flux from Lancang River Basin (LRB, Chinese part of LMRB) to lower LMRB (other parts of LMRB). The results showed that the Total Phosphorus load in the LRB is about 27,079 tons/year, of which 85% TP is collected from July to October. The annual TP export at the outlet of the LRB is 14,112 tons/year under no-dam scenario, which accounts for about 4.2% of the total TP loads in the lower LMRB. With seven to twenty-one dams included in experiments, TP flux at the outlet of the LRB decreased 50–59%, while the delivered ratio for the lower LMRB decreased 2.1–2.5%. As a summary, building dams has a significant impact on the TP transport pattern in the Chinese part of LMRB, but very limited effect in lower LMRB according to the modeling results, especially for the Mekong delta. Moreover, the existing dams (seven dams) seem to intercept much more phosphorus than those dams that are under construction.