Dissolved Phosphorus Concentrations Research Articles

Rapid response of stream dissolved phosphorus concentrations to wildfire smoke

Wildfires can produce large plumes of smoke that are transported across vast distances, altering nutrient cycling of undisturbed watersheds exposed downwind. To date, wildfire smoke influence on stream biogeochemical signatures remains an important knowledge gap. Here we evaluate the impacts of wildfire smoke on phosphorus (P) biogeochemical cycling in a temperate watershed in the Finger Lakes Region of Central New York located downwind from record setting Canadian forest fires during the summer of 2023. Daily sampling of stream and rainwaters was conducted over the 2 month smoke period, generating a robust geochemical dataset. Stream dissolved P showed high sensitivity to smoke events, attaining concentrations 2–3 × greater than the pre-smoke period. Subsequent rain events after smoke deposition were identified as a potentially important factor in magnitude and timing of dissolved P responses. These findings demonstrate the capacity for wildfire smoke to trigger rapid, observable changes to stream P chemistry.

Characterization of runoff phosphorus loss from a combination of long-term fertilizer application and cultivation on sloping croplands

Study regionPurple soil sloping cropland, a representative landscape in the upper reaches of the Yangtze River, and is the main distributed agricultural basis of the Sichuan Basin, Southwest China. Study focusThis study investigated the responses of runoff P loss to several rainfall categories, the combined application of manure and chemical fertilizers, and contour cultivation by analyzing 120 rainfall events that transpired between 2008 and 2022 on a representative purple soil sloping cropland. There were five treatment combinations utilized in this study: no fertilizer application with downslope cultivation (CK), chemical fertilizer application with downslope cultivation (T1), manure and chemical fertilizer application with downslope cultivation (T2), 1.5-fold chemical fertilizer application with downslope cultivation (T3), and chemical fertilizer application with contour cultivation (T4). New hydrological insight of the regionThe runoff depth during large rainstorms was significantly higher (21.5–252.4 %) than that of other rainfall categories (p < 0.05). Dissolved phosphorus (DP) loss was highest during rainstorms, whereas the highest particulate phosphorus (PP) loss was observed during large rainstorms. The runoff depth and sediment yield were significantly higher in CK than those in other treatments (p < 0.05). There were significant linear relationships between runoff depth and PP loss, DP concentration (p < 0.05). The results of this study have great significance in improving our understanding of the characteristics associated with runoff P loss in sloping croplands in Southwest China.

Response of runoff N and P concentrations, losses, and stoichiometry to rainfall amount category, multisource fertilization, and straw return in sloping croplands

Nitrogen (N) and phosphorus (P) losses via runoff from sloping croplands are a major threat to the degradations of soil fertility and water quality worldwide. Rainfall amount category and agricultural practices, such as multisource fertilization and straw return, are key factors regulating nutrient loss via runoff in sloping croplands. Yet, the impacts of these factors on N and P losses via runoff remain elusive. This study investigated the responses of N and P in runoff to rainfall amount category, multisource fertilization, and the combination of multisource fertilization and straw return in sloping cropland with a radish and maize rotation during multiple natural rainfall events between 2019 and 2021. Three agricultural treatments (three replications for each), i.e., local traditional fertilization (CK), multisource fertilization (T1), and a combination of T1 and straw return (T2), were applied on nine 8 m × 3 m plots. The concentrations and losses of total nitrogen (TN), total phosphorus (TP), dissolved nitrogen (DN), dissolved phosphorus (DP), particulate nitrogen (PN) and particulate phosphorus (PP) and their paired stoichiometries in runoff were determined. The runoff depth during rainstorms was similar to that in large rainstorms and was 191.1 % and 178.7 % higher than in moderate and heavy rains, respectively (p < 0.05). The PN concentration was the highest during moderate rain, and the highest concentrations of TP and DP were observed during large rainstorms (p < 0.05). Rainstorms and large rainstorms produced higher runoff losses for PN, TP, DP, and PP than for other rainfall amount categories (p < 0.05). Compared to CK, the runoff depth was marginally reduced by 4.2 % and 12.7 % in T1 and T2, respectively, and the concentrations and losses of N and P in runoff also slightly increased in T1 and T2. The DN and DP losses accounted for 70.5 % and 59.8 % of the TN and TP losses across all treatments, respectively, indicating that the dissolved forms played a dominant role in nutrient loss via runoff. TN:TP (77:1) in runoff was higher than the Redfield ratio (16:1) across all treatments, implying a stoichiometric potential for P depletion in the runoff. Our results highlight the potential risk of N and P losses in dissolved form via runoff regulated by rainfall, multisource fertilization and straw return in sloping croplands.

Cyanotoxins bioaccumulation by fish in an anthropized reservoir in central Mexico

The bioaccumulation of cyanotoxins has been well documented in exposed organisms including fish, which represent a potential route to cyanotoxins transfer to humans by consumption of contaminated food. We determined the bioaccumulation of neurotoxic saxitoxins and hepatotoxic microcystins in muscle and liver/viscera of native (Goodea atripinnis), introduced (Poeciliopsis gracilis), and commercially important (Oreochromis niloticus) fish in Santa Catarina, an anthropized reservoir in Central Mexico. Additionally, we calculated the potential risk of human exposure due to the consumption of the studied species. The Santa Catarina Reservoir showed some physical and chemical water parameters generally associated with cyanobacterial blooms (e.g., high phycocyanin, chlorophyll-a, dissolved phosphorus concentrations, and alkaline pH) with presence of cyanotoxins produced by the cyanobacteria genera Microcystis, Dolichospermum, and Planktothrix, which were found in dissolved and particulate (sestonic) fractions of water. Moreover, we detected the presence of saxitoxins and microcystins in the tissues of all species studied. The risk of intoxication for humans was lower for the consumption of Nile tilapia muscle than for the other analyzed species, whose consumption should be avoided since it exceeds the recommended daily intake of microcystins for a short-term (i.e., two-week exposure time). These findings are remarkable because commercial fishing in reservoirs and the consumption of these fish could represent a route to human exposure to toxins, particularly microcystins. Our results highlight the need for the detection of cyanotoxins and the evaluation of their bioaccumulation by fish in unstudied eutrophic waterbodies, to reduce the potential health risk for humans and the environment.

Management of eutrophication using combined the “flock &amp; sink” mitigation technique and submerged plants restoration: a mesocosm study

Abstract Currently, the issue of eutrophication and cyanobacterial blooms persists in water bodies worldwide, prompting the exploration of various treatment methods. This study conducted a comparative analysis of eutrophic water bodies using ferric chloride-modified zeolite (FMZ) and calcium hydroxide-modified zeolite (CMZ) combined with Elodeanuttallii (E. nuttallii) for removal and purification effects. The results revealed that the addition of E. nuttallii had a sustained inhibitory effect on phosphorus release, maintaining stability with lower Turbidity(Tur) and stabilized pH within the range of 8.5-9. FMZ demonstrated rapid reduction in dissolved phosphorus concentration, achieving a removal rate of 96% within 3 days. The combined plant group of CMZ and FMZ exhibited synergistic effects with E. nuttallii, achieving an impressive total phosphorus (TP) removal rate of 80.13% and a total nitrogen (TN) removal rate of 48.77%. Additionally, chlorophyll a (Chl a) concentration decreased from 100.74 ± 24.72 μg/L to 49.96 ± 2.08 μg/L. The phytoplankton community composition indicated that diatoms thrived in low temperatures and high NH4 conditions. Under the same low Total Nitrogen to Total Phosphorus (TN:TP) ratio, high TP concentrations were associated with cyanobacteria dominance, while green algae dominated in other scenarios. This comprehensive approach demonstrates the potential efficacy of CMZ and FMZ combined with E. nuttallii in addressing eutrophic water bodies and mitigating cyanobacterial blooms.

Predicting nature recovery for river restoration planning and ecological assessment: A case study from England, 1991–2042

AbstractThe Global Biodiversity Framework established ambitious goals for nature recovery which governments must now incorporate into national legislation. In England, legally binding targets require authorities to halt the decline in species abundance by 2030 and reverse the decline by 2042. Riverine invertebrates represent a substantial proportion of the species contributing towards the targets. Thus, understanding the response of these species to potential river restoration actions is key to target delivery. We model counts for 188 riverine invertebrate taxa using zero‐inflated generalized Poisson models, applying the models to both inform river restoration planning and set expected values for use in ecological assessment. We identify catchment‐specific restoration strategies that combine one or more actions involving the removal of channel modifications, reductions in nitrate concentrations and reductions in total dissolved phosphorus concentrations as the most likely to deliver species abundance targets across three joint climate–socioeconomic scenarios. By hindcasting species abundances under alternative target frameworks, we also demonstrate a new approach to setting expected values in ecological assessment, accounting for changes in water temperature and hydrology that confound historical reference models presently used by regulators. Our findings represent the first systematic attempt to prioritise major actions to deliver species abundance targets in England, providing valuable insights for policymakers, river restoration practitioners and authorities responsible for monitoring river ecosystems.

Historical Phosphorus Mass and Concentrations in Utah Lake: A Case Study with Implications for Nutrient Load Management in a Sorption-Dominated Shallow Lake

Utah Lake is unusual due to its large surface area, shallow depth, phosphorus-rich sediments, and well-mixed, unstratified waters. This creates conditions where water column phosphorous concentrations tend toward equilibrium, with lake sediments containing high concentrations of geologic phosphorus. To help understand the potential impact of phosphorous load reductions, we computed a time history of phosphorus mass in the lake using state and federal records of lake volume, dissolved phosphorus concentrations, and outflow. We show that historically, Utah Lake phosphorus concentrations have remained stable over time, in the range of 0.02 to 0.04 mg/L, despite large changes in lake volume and internal phosphorus mass. We performed sorption calculations using data from the literature, demonstrating that it would take unrealistically large load changes to alter water column phosphorus concentrations under sorption processes. The sorption model produces results consistent with historical data that show relatively constant phosphorous concentrations despite large lake volume changes. We show, through several lines of evidence, that water column phosphorus concentrations are insensitive to external loads. Phosphorous load reduction is unlikely to have a significant effect on phosphorus concentrations in Utah Lake and, by extension, in other sorption-dominated shallow lakes with phosphorus-rich sediment.

Effects of Dielectric Barrier on Water Activation and Phosphorus Compound Digestion in Gas-Liquid Discharges.

To generate a stable and effective air-liquid discharge in an open atmosphere, we investigated the effect of the dielectric barrier on the discharge between the pin electrode and liquid surface in an atmospheric-pressure plasma reactor. The atmospheric-pressure plasma reactor used in this study was based on a pin-plate discharge structure, and a metal wire was used as a pin-type power electrode. A plate-type ground electrode was placed above and below the vessel to compare the pin-liquid discharge and pin-liquid barrier discharge (PLBD). The results indicated that the PLBD configuration utilizing the bottom of the vessel as a dielectric barrier outperformed the pin-liquid setup in terms of the discharge stability and that the concentration of reactive species was different in the two plasma modes. PLBD can be used as a digestion technique for determining the phosphorus concentration in natural water sources. The method for decomposing phosphorus compounds by employing PLBD exhibited excellent decomposition performance, similar to the performance of thermochemical digestion-an established conventional method for phosphorus detection in water. The PLBD structure can replace the conventional chemical-agent-based digestion method for determining the total dissolved phosphorus concentration using the ascorbic acid reduction method.

Co-precipitation of iron and silicon: Reaction kinetics, elemental ratios and the influence of phosphorus

A sufficient supply of dissolved silicon (DSi) relative to dissolved phosphorus (DP) may decrease the likelihood of harmful algal blooms in eutrophic waters. Oxidative precipitation of Fe(II) at oxic-anoxic interfaces may contribute to the immobilization of DSi, thereby exerting control over the DSi availability in the overlying water. Nevertheless, the efficacy of DSi immobilization in this context remains to be precisely determined. To investigate the behavior of DSi during Fe(II) oxidation, anoxic solutions containing mixtures of aqueous Fe(II), DSi, and dissolved phosphorus (DP) were exposed to dissolved oxygen (DO) in the batch system. The experimental data, combined with kinetic reaction modeling, indicate that DSi removal during Fe(II) oxidation occurs via two pathways. At the beginning of the experiments, the oxidation of Fe(II)-DSi complexes induces the fast removal of DSi. Upon complete oxidation of Fe(II), further DSi removal is due to adsorption to surface sites of the Fe(III) oxyhydroxides. The presence of DP effectively competes with DSi via both of these pathways during the initial and later stages of the experiments, with as a result more limited removal of DSi during Fe(II) oxidation. Overall, we conclude that at near neutral pH the oxidation of Fe(II) has considerable capacity to immobilize DSi, where the rapid homogeneous oxidation of Fe(II)-DSi results in greater DSi removal compared to surface adsorption. Elevated DP concentration, however, effectively outcompetes DSi in co-precipitation interactions, potentially contributing to enhanced DSi availability within aquatic systems.

Dissolved phosphorus concentrations are increasing in streams across the Great Lakes Basin

Dissolved phosphorus concentrations are increasing in streams across the Great Lakes Basin

Phosphorus in shallow and deep groundwater: Importance of P/Fe ratio in Fe(III) oxides in aquifer sediments

The causes of the differential enrichment of dissolved phosphorus (P) in the shallow and deep aquifers remain elusive. In this study, groundwater and aquifer sediments were sampled from the Songnen Basin to explore the behaviour and mobilization mechanism of P in a shallow sandy aquifer and a deep sand-gravel aquifer by means of hydrogeochemical analyses and characterizations of dissolved organic matter (DOM) and sedimentary Fe minerals. The results showed that both aquifers were enriched in dissolved P, being mainly related to the organic matter degradation and Fe(III) oxides reduction. Comparatively, total dissolved phosphorus concentrations in shallow groundwater were significantly higher than those in the deep one (p < 0.01), owing to the stronger extent of reductive dissolution of Fe(III) oxides with higher P/Fe molar ratio in the shallow aquifer. Moreover, groundwater DOM with more humic substances in the shallow aquifer promoted the P mobilization via electron shuttling and/or competitive adsorption. In the deep aquifer, reductive dissolution of Fe(III) oxides with high P content resulted in the enrichment of groundwater P. In the two aquifers, immobilization of P via Fe(II) mineral precipitation played a minor role in the fate of groundwater P. This study underlines that geogenic enrichment of P in groundwater can occur in the sand-gravel aquifers with high contents of P and Fe(III) oxides under reducing conditions, and highlights that P/Fe molar ratio in Fe(III) oxides is the most important factor controlling dissolved P in groundwater systems.

Dissolved organic matter transformations in a freshwater rivermouth

River-to-lake transitional areas are biogeochemically active ecosystems that can alter the amount and composition of dissolved organic matter (DOM) as it moves through the aquatic continuum. However, few studies have directly measured carbon processing and assessed the carbon budget of freshwater rivermouths. We compiled measurements of dissolved organic carbon (DOC) and DOM in several water column (light and dark) and sediment incubation experiments conducted in the mouth of the Fox river (Fox rivermouth) upstream from Green Bay, Lake Michigan. Despite variation in the direction of DOC fluxes from sediments, we found that the Fox rivermouth was a net sink of DOC where water column DOC mineralization outweighed the release of DOC from sediments at the rivermouth scale. Although we found DOM composition also changed during our experiments, alterations in DOM optical properties were largely independent of the direction of sediment DOC fluxes. We found a consistent decrease in humic-like and fulvic-like terrestrial DOM and a consistent increase in the overall microbial composition of rivermouth DOM during our incubations. Moreover, greater ambient total dissolved phosphorus concentrations were positively associated with the consumption of terrestrial humic-like, microbial protein-like, and more recently derived DOM but had no effect on bulk DOC in the water column. Unexplained variation indicates that other environmental controls and water column processes affect the processing of DOM in this rivermouth. Nonetheless, the Fox rivermouth appears capable of substantial DOM transformation with implications for the composition of DOM entering Lake Michigan.

The application of biochar mitigated the negative effects of freeze-thaw on soil and nutrient loss in the restored soil of the alpine mining area

Mining operations accelerate ecological damage in alpine mountain locations by contributing to soil erosion and nutrient loss in the freeze-thaw (FT) climate. However, limited studies have been conducted to reduce the soil erosion and nutrient loss in FT climate. This study’s goal was to determine how biochar effected soil erosion in the restored soil of the alpine mining region under FT circumstances. Rainfall simulation and FT cycles (FTCs; three and 5) were used to investigate the effects of 500 and 1,000 kg hm−2 biochar application rates (BARs) on runoff, soil loss, and runoff loss of ammonia nitrogen (AN), nitrate nitrogen (NN), total phosphorus (TP), and dissolved phosphorus (DP). Soil residual AN, NN, and DP concentrations after FTCs were also evaluated. Biochar application significantly reduced the runoff, soil loss rate, AN and NN loss rates, but increased the runoff NN concentration and decreased the total AN and NN loss under FTCs condition. Reductions in AN (37.2%–52.2%) and NN (14.3%–27.1%) runoff loss can be differentially attributed to the adsorption effect of biochar and decrease in total runoff. The runoff P concentrations, rates, and magnitudes for soils subjected to FTCs significantly decreased with biochar addition, owing to the particulate P loss decrease in soil and increased adsorption effect of soil DP. Biochar addition increased soil residual AN, NN, and DP concentrations. However, the increase in FTCs weakened the inhibitory effects of biochar on soil erosion. This study suggested the important role of biochar application for the recovery of low-nutrient eroded soils in alpine mining areas.

Seasonal Variability of Phytoplanktons in the Non-Point Source Polluted River Nggada, Maiduguri – Borno State, Nigeria

Borno State is the epicenter of Boko Haram crisis which displaced millions of individuals. Maiduguri metropolis which became the principal refuge centre, has witnessed a rapid demographic change, land use and economic activities resulting into intense irrigational practice along the bank of river Nggada. This may result into changes in the physico – chemical parameters of the aquatic ecosystem and the dynamism may disrupt phytoplantonic community. The study was aimed at assessing the seasonal variability of phytoplanktons in non-point source polluted river Nggada of Maiduguri. Water samples for physico -chemical analysis were collected bi-weekly for a period of 11 months at three sampling stations. Physico-chemical parameters, including Dissolve Oxygen (DO), Dissolved Nitrate concentration, Dissolved Phosphorus Concentration, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Surface Water Temperature (SWT) and potential Hydrogen (pH) were determined using standard procedures. Results indicated that all physico – chemical parameters except temperature, DO and pH of the river during both irrigational and non-irrigational regimes were slightly above the National Environmental Standards and Regulations Enforcement Agency’s (NESREA) permissible limits. A total of 7 classes (Cyanophyceae Chlorophyceae, Cryptophyceace, Euglenophyceae, Bacillariophyceae, Crysophyceace and Rhodophyceae) and 16 genera of phytoplanktons were identified. The results further revealed that the irrigation activities (dry season) have impacted on the physico – chemical parameters (pH, DO, TDS, nitrate and phosphate concentrations) of the study area. Remarkably, the changes in the physico – chemical parameters during the irrigational regime (dry season) have not impacted on the abundance and distribution of phytoplanktons. Hence, the non-point pollutants influenced the physico – chemical parameters of the river butalgal abundance and distribution were not influenced by the changes in the physico – chemical parameters of the river. The study thus, recommends the continuous monitoring and systematic effort to conserve the bio-resources and water quality of the river

Effects of Phosphorus Fertilizer Application Rates on Colloidal Phosphorus Leaching in Purple Soil in Southwest China

Phosphorus (P) lost via leaching from agricultural land is of major concern for water resource managers worldwide, and colloidal phosphorus (CP) may have a high contribution, since it is an important mobile form of P in soil and subsurface drainage. The objective of this study is to relate P fertilization application rates to CP leaching. To eliminate the influence of climate and facilitate the accurate measurement of P contents in different soil layers, we established soil columns to investigate the impacts of fertilizer application rates and timing on P leaching. Therefore, a soil column leaching experiment was undertaken with different P fertilization application rates (0, 20, 40, 100, 200, and 400 mg kg−1) for purple soil in southwest China. P application rates had significant effects on CP and dissolved phosphorus concentrations in the top soils (p &lt; 0.05) (e.g., 0–10 cm in this study), and they further increased P leaching loss by 24–375%. CP was the dominant P form and contributed 31–61% to total phosphorus in the leachate. The concentration of different P forms in leachates decreased significantly over time, and the risk of P leaching loss was greater within two weeks after P application (p &lt; 0.05). The advisable range of P application rate is recommended to be 0–450 kg ha−1 for agricultural practice, and it is also recommended to keep P fertilizer in the soil for more than two weeks. Some countermeasures, related to application rates and timing, should be taken to minimize the buildup of P in the field and reduce the risk of P leaching.

Dissolved Phosphorus Concentrations in Surface Runoff from Agricultural Land Based on Calcium–Acetate–Lactate Soluble Phosphorus Soil Contents

The input of phosphorus (P) into aquatic systems can result in eutrophication that might manifest in algal blooms and oxygen deficiency and, subsequently, in a poor ecological status. Substance emission modeling on a river basin scale can help to quantify phosphorus emissions into surface water bodies and to address mitigation measures. The prerequisite is that suitable input data are available. The purpose of this study is to develop a modeling approach that allows the prediction of realistic phosphorus concentrations in surface runoff. During large-scale artificial rain experiments at 23 agricultural sites, dissolved P concentrations in surface runoff and subsurface flow were measured. The characteristics of the experimental sites were investigated by taking and analyzing soil samples and requesting information on the management from the farmers. From the data collected, two linear models were derived. The first model allows the prediction of dissolved phosphorus concentration in surface runoff from PCAL soil content. Applying the second model, the obtained concentration in surface runoff can be transferred to a concentration in subsurface flow. The resulting approaches were derived from realistic field experiments and, for the first time, allow the direct prediction of dissolved phosphorus concentrations in surface runoff and, in a second step, also in subsurface flow from spatially distributed PCAL soil content data. Integrating these approaches into substance emission models can improve their accuracy and, subsequently, allows a better planning of measures for the reduction in phosphorus emissions into surface water bodies.

Some Traits of Meiofauna in the Surf Region of the Southern Mediterranean Sea Coast

During the winter and summer of 2019, eight study sites in eastern Libya were used to establish meiofauna diversity in the Southern Mediterranean Sea's near-shore sandy bottom surf region. The physicochemical characteristics of surface water at the study sites were mostly similar. Seventeen taxa of floatable meiofauna (extracted from sediment samples by floatation) were identified, sixteen during winter and ten during summer: By number of individuals per taxon, Nematoda and Foraminifera were the most abundant taxa. The other available taxa were Rhabdocoela, Xanacoelomorpha, Gastrotrichs, Polychaeta, Kinorhyncha, and Urodasys. Four non-floatable meiofauna taxa were encountered (Foraminifera, Mussel, Gastropod, and Ostracoda). This low diversity of floatable and non-floatable meiofauna was possibly due to the strong wave action prevailing in the region and the adjacent deleterious anthropogenic activities. Meiofaunal diversity was higher in winter than in summer, possibly due to the higher dissolved phosphorus concentration during this season. The causes of the between-site differences in meiofaunal diversity are unclear, but differences in adjacent coastal anthropogenic activities might had more impact than differences in the prevailing physicochemical traits of the interstitial habitat. New practical techniques for collecting and identifying the smaller meiofauna are needed.

Environmentally induced functional shifts in phytoplankton and their potential consequences for ecosystem functioning

Phytoplanktonic organisms are particularly sensitive to environmental change, and, as they represent a direct link between abiotic and biotic compartments within the marine food web, changes in the functional structure of phytoplankton communities can result in profound impacts on ecosystem functioning. Using a trait-based approach, we examined changes in the functional structure of the southern North Sea phytoplankton over the past five decades in relation to environmental conditions. We identified a shift in functional structure between 1998 and 2004 which coincides with a pronounced increase in diatom and decrease in dinoflagellate abundances, and we provide a mechanistic explanation for this taxonomic change. Early in the 2000s, the phytoplankton functional structure shifted from slow growing, autumn blooming, mixotrophic organisms, towards earlier blooming and faster-growing microalgae. Warming and decreasing dissolved phosphorus concentrations were linked to this rapid reorganization of the functional structure. We identified a potential link between this shift and dissolved nutrient concentrations, and we hypothesise that organisms blooming early and displaying high growth rates efficiently take up nutrients which then are no longer available to late bloomers. Moreover, we identified that the above-mentioned functional change may have bottom-up consequences, through a food quality-driven negative influence on copepod abundances. Overall, our study highlights that, by altering the phytoplankton functional composition, global and regional changes may have profound long-term impacts on coastal ecosystems, impacting both food-web structure and biogeochemical cycles.

Remote monitoring of total dissolved phosphorus in eutrophic Lake Taihu based on a novel algorithm: Implications for contributing factors and lake management

Understanding the spatiotemporal dynamics of total dissolved phosphorus concentration (CTDP) and its regulatory factors is essential to improving our understanding of its impact on inland water eutrophication, but few studies have assessed this in eutrophic inland lakes due to a lack of suitable bio-optical algorithms allowing the use of remote sensing data. We developed a novel semi-analytical algorithm for this purpose and tested it in the eutrophic Lake Taihu, China. Our algorithm produced robust results with a mean absolute square percentage error of 29.65% and root mean square error of 9.54 μg/L. Meanwhile, the new algorithm demonstrates good portability to other waters with different optical properties and could be applied to various image data, including Moderate Resolution Imaging Spectroradiometer (MODIS), Medium Resolution Imaging Spectrometer (MERIS), and Ocean and Land Color Instrument (OLCI). Further analysis based on Geostationary Ocean Color Imager observations from 2011 to 2020 revealed a significant spatiotemporal heterogeneity of CTDP in Lake Taihu. Correlation analysis of the long-term trend between CTDP and driving factors demonstrated that air temperature is the dominant regulating factor in variations of CTDP. This study provides a novel algorithm allowing remote-sensing monitoring of CTDP in eutrophic lakes and can lead to new insights into the role of dissolved phosphorus in water eutrophication.

Nutrient dynamics in stream water and groundwater in riparian zones of a mesoscale agricultural catchment with intense seasonal pumping

Water and soil in agricultural areas are usually enriched with nutrients from excessive fertilizations. Riparian zones, the interfaces between terrestrial and aquatic systems, play crucial roles in delivery of the nutrients to groundwater and surface water. We evaluated spatiotemporal variations of water flow and nutrients in a mesoscale agricultural catchment along the riparian zones of the main stream for dry and rainy season by hydrologic monitoring and measurements of hydrochemical parameters and water stable isotopes. Gaining stream conditions were dominant in the mountainous upper reaches with steep topographic gradient while groundwater level in the lower basin considerably varied seasonally due to intense groundwater pumping to aid in heating greenhouses in winter season, which resulted in losing stream conditions during the dry season. Compared to shallow groundwater, deep groundwater had higher nitrate concentration derived from dry farmland in hilly terrains and induced recharge due to the groundwater pumping. Nitrate concentration was significantly higher in groundwater than that in stream water, indicating that groundwater is a major source of nitrate in stream water considering mainly gaining stream conditions. Compared to stream water, dissolved phosphorus concentration was higher in shallow groundwater recharged from paddy fields and floodplain areas with reducing conditions, evaporation signature of water stable isotopes, and lower nitrate concentration. Nutrient flux estimates for the catchment revealed that nitrate in stream water is considerably contributed by groundwater discharge and shallow groundwater in reducing conditions is a significant source of dissolved phosphorus in stream water, which was more pronounced in the rainy season. This study demonstrated that intense agricultural activities in riparian zones strongly affect stream-aquifer interactions and nutrient delivery to the stream, as well as groundwater. These findings can contribute to understanding hydrological and biogeochemical processes of nutrients in agricultural catchments and establishing an effective management of water use and nutrient application.