Soluble Reactive Phosphorus Levels Research Articles

Evaluation of the dynamics of nutrients and potentially toxic elements along a major river in Ethiopia using multivariate statistical techniques: Implications of possible co-occurrences

This study utilized established field and laboratory methods and multivariate statistical tools to evaluate the nutrient and potentially toxic elements (PTEs) distribution, identify possible sources, and determine potential co-existence in the Awash River. The levels of soluble reactive phosphorus (SRP), total phosphorus (TP), NO3-N, Mn, Ni, Cr, and Cu generally increased downstream in the upper Awash, with the highest respective values of 0.70, 1.34, 1.19, 1.58, 1.03, 0.85, and 0.11 mg L−1 at the inlet to Lake Koka. Sites found downstream of the inflow of Lake Beseka and Metehara town showed the highest levels of Fe, B, Zn, and dissolved silica. Principal components and correlation analysis findings revealed strong associations (r ≥ 0.80, p < 0.05) between nutrient parameters (SRP, TP, and NO3-N) and PTEs (Cu, Ni, Mn, and Cr), implying common origins and potential co-occurrences. The potential co-occurrences of these parameters may strengthen their potential individual impacts due to complex interactions.

Fine-scale measurements unravel the side effects of biochar capping on the bioavailability and mobility of phosphorus in sediments

Biochar is widely used for sediment remediation owing to its excellent adsorption properties and low carbon footprint. However, the impacts of biochar capping on phosphorus (P) bioavailability and mobility in the sediment are little known. In this study, the P mobilization processes in sediments capped with biochar were investigated by combining advanced high-resolution sampling techniques and microbiome analysis. The results showed that biochar is a double-edged sword for the sediment P release, depending on the application dosage and the capping time. In the short term (30 days), 2-cm biochar capping decreased the release flux of soluble reactive phosphorus (SRP) by 73.1%, whereas the 1-cm biochar capping significantly increased the release flux of SRP by 51.0%. After aging of biochar (80 days), the resupply capacity of sediment P was improved, resulting in increases of more than 33.7% and 121.5% in the release fluxes of SRP in the 1-cm and 2-cm capping groups, respectively, compared to the control group. Chemisorption played a pivotal role in regulating the levels of SRP, particularly during the short-term capping period. And more biochar can provide more adsorption sites on P. The P mobilization increase could be attributed to P desorption from biochar after biochar aging. Furthermore, biochar capping intensified the microbial-mediated iron reduction and organic matter decomposition, which enhanced P mobility. Our study highlights the importance of biochar application dosage and the capping time in sediment remediation, providing a scientific basis for the optimization of biochar capping techniques.Graphical

Seasonal variability of CO2, CH4, and N2O content and fluxes in small agricultural reservoirs of the northern Great Plains

Inland waters are important global sources, and occasional sinks, of CO2, CH4, and N2O to the atmosphere, but relatively little is known about the contribution of GHGs of constructed waterbodies, particularly small sites in agricultural regions that receive large amounts of nutrients (carbon, nitrogen, phosphorus). Here, we quantify the magnitude and controls of diffusive CO2, CH4, and N2O fluxes from 20 agricultural reservoirs on seasonal and diel timescales. All gases exhibited consistent seasonal trends, with CO2 concentrations highest in spring and fall and lowest in mid-summer, CH4 highest in mid-summer, and N2O elevated in spring following ice-off. No discernible diel trends were observed for GHG content. Analyses of GHG covariance with potential regulatory factors were conducted using generalized additive models (GAMs) that revealed CO2 concentrations were affected primarily by factors related to benthic respiration, including dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), dissolved organic carbon (DOC), stratification strength, and water source (as δ18Owater). In contrast, variation in CH4 content was correlated positively with factors that favoured methanogenesis, and so varied inversely with DO, soluble reactive phosphorus (SRP), and conductivity (a proxy for sulfate content), and positively with DIN, DOC, and temperature. Finally, N2O concentrations were driven mainly by variation in reservoir mixing (as buoyancy frequency), and were correlated positively with DO, SRP, and DIN levels and negatively with pH and stratification strength. Estimates of mean CO2-eq flux during the open-water period ranged from 5,520 mmol m−2 year1 (using GAM-predictions) to 10,445 mmol m−2 year−1 (using interpolations of seasonal data) reflecting how extreme values were extrapolated, with true annual flux rates likely falling between these two estimates.

Higher Levels of Soluble Reactive Phosphorus Promote Labile Organic Nitrogen Cycling in Subsurface Coastal Waters

AbstractRemineralization of labile organic nitrogen is a key part of nitrogen cycling in seawater, yet factors controlling this process remain poorly understood. The degradation and fate of amino acids in coastal waters were investigated with incubation experiments using 15N‐labeled alanine (Ala). The cycling of Ala, including the release of NH4+ through remineralization, the subsequent removal of NH4+ via assimilation and nitrification, and the formation of refractory dissolved organic nitrogen (DON), was more rapid in subsurface (mid‐depth 8 m and bottom 17 m) than in surface coastal waters (2 m) of the northern Gulf of Mexico in summer. This pattern is attributed to the different levels of soluble reactive phosphorus (SRP) observed at different depths of the water column. The addition of orthophosphate to the surface water with low SRP (&lt;0.1 μmol L−1) significantly accelerated the remineralization of amino acid, nitrification, and the formation of refractory DON. The rapid remineralization of amino acid and further nitrification in SRP‐replete waters are linked to the rapid growth of heterotrophic bacteria and ammonia‐oxidizing archaea, respectively. Taken together, these results suggest that subsurface coastal waters enriched with SRP are pre‐primed for rapid organic N metabolisms, providing mechanistic insights into nitrogen cycling in marine waters.

Influence of surface geology on phosphorus export in coastal forested headwater catchments in Akita, Japan

ABSTRACT Surface geology is a key factor regulating the geographical patterns of P export; however, geographically extensive data on P export mechanisms from natural coastal mountain regions are lacking. We compared stream-water characteristics in forested headwater catchments with different types of surface geology (marine sedimentary rocks [MSRs] and igneous rocks [IRs]) and evaluated the factors regulating soluble reactive phosphorus (SRP) concentrations in stream water. Geographically extensive stratified sampling was conducted: stream-water and sediment samples were obtained from 66 MSR catchments and 55 adjacent IR catchments along the coastal forested mountain regions in Akita, Japan. SRP and major cations and anions in stream waters were analyzed. To evaluate the effect of ionic composition on SRP, sediments were extracted with NaCl and CaCl2 solutions and the SRP concentrations in the extracts were measured. Stream SRP was significantly higher in MSR catchments (median 23 µg L−1) than in IR catchments (median 8 µg L−1) (P < 0.001), and tended to be higher in MSR catchments with younger rocks. Dissolved inorganic nitrogen (DIN) did not differ between catchments with different geologies; therefore, DIN/SRP was significantly lower in MSR catchments (median 18), close to the Redfield ratio. On a Piper diagram, high-SRP stream waters were of the NaCl water type, and stream SRP was significantly correlated with Na+ (r = 0.642, P < 0.0001). In IR catchments, stream waters had relatively higher Ca2+ and Mg2+ concentrations. SRP in the sediment extracts was significantly higher in MSR catchments and samples obtained by NaCl extraction than in IR catchments and CaCl2-extracted samples. Exchangeable Na+ in sediments was significantly higher in MSR catchments, decreasing Ca2+ in the liquid phase by an ion-exchange reaction, which is likely also key in maintaining high SRP levels. We conclude that MSR catchments in coastal Akita are a significant P source for streams even in headwater forests, and that site-specific NaCl water types and higher exchangeable Na+ concentrations in sediments result in higher SRP concentrations in stream waters. These results have critical implications for P cycles in freshwater ecosystems influenced by Na+.

The effect of natural materials used as sediment remediation on phosphorus and nitrogen control in a mesocosm

BackgroundAchieving nitrogen (N) and phosphorus (P) control in sediment remediation projects by adding natural materials is receiving increasing attention. In this study, different natural materials, including iron-rich clay minerals, calcite, kaoline, sugarcane bagasse and Phragmites detritus, were applied to test their effects on N and P in a mesocosm experiment.ResultsIron-rich clay minerals and Phragmites detritus had obvious advantages for P control; they resulted in almost undetectable levels of soluble reactive phosphorus (SRP) in the water column throughout the experiment. This finding can be explained by their strong P adsorption ability. The high level of available organic carbon in the sediment and water column after sugarcane bagasse addition provided enough electron donors for denitrification and dissimilatory nitrate reduction to ammonium (DNRA), which caused nitrate (NO3−-N) deficiency and ammonium (NH4+-N) accumulation in the water column. Additionally, this resulted in anaerobic conditions, further fuelling the release of P from iron-bound P induced by anoxia. Thus, the amount of sugarcane bagasse applied should be considered carefully in order to balance denitrification and DNRA as well as P releases. Calcite and Phragmites detritus are recommended as remediation materials for N removal based on their significant promotion of denitrification and limitation of DNRA, which resulted in low NO3−-N and NH4+-N levels. These results can be explained by the shifts in the functional microbial community composition and abundance after the addition of natural materials.ConclusionsIron-rich clay minerals and Phragmites detritus are promising sediment remediation materials for P immobilization due to their strong P adsorption ability. Taken together, the selection of sediment remediation materials should consider the N and P coupling relationship, to prevent NO3−-N removal from causing P leaching or NH4+-N accumulation.

Didymosphenia geminata blooms are not exclusively driven by low phosphorus under experimental conditions

Despite two decades of research, the cause of blooms of the diatom Didymosphenia geminata remains uncertain. Blooms have been associated with low nutrient, oligotrophic streams. In this study, we used available data from across the globe and conducted experiments to determine how D. geminata responds to soluble reactive phosphorus (SRP) concentrations. Globally, D. geminata blooms have been found in streams with SRP below 11 μg P l−1. In North America, blooms only occurred at high equivalent latitudes when SRP was very low, whereas at lower latitudes blooms were observed under higher SRP concentrations. Using an in situ experiment, we found that following physical removal of D. geminata from stones, regrowth did not occur despite low SRP concentrations. In a second experiment, we found that there were no differences in D. geminata growth between a treatment which depleted SRP and a treatment which maintained elevated springtime SRP levels. These findings indicate that D. geminata blooms do not always form when SRP is low, even when cells are present. Bloom formation that is not exclusively related to low SRP suggests additional chemical or biotic factors, specific physical conditions, a seasonal timing requirement, or some combination of these with low P that are necessary to produce blooms.

Two mathematical approaches to study the phosphorus eutrophication of a wetland in Puerto Rico

Introduction: Laguna Cartagena (LC), a wetland in Lajas, Puerto Rico, has been negatively impacted by nutrients, mainly phosphorus run-off from agricultural activities until the end of sugar cane cultivation in the late 1900s. This led to P concentration remain high at hypereutrophic state that was irremediable even after a 5-fold reduction in source water nutrient concentration.&#x0D; Objective: The main goal of this research paper is to apply two different mathematical approaches to assess the eutrophication level of a wetland in Puerto Rico.&#x0D; Method: Grey Cluster Method (GCM) was used to classify LC’s eutrophic state by applying the International and Chinese trophic standards and two parameters, total phosphorous (TP) and total nitrogen (TN). Mean TP and TN from LC consolidated bottom substrate and flocculence samples were used to classify LC. To address whether LC can recover, soluble reactive phosphorus (SRP) and TP from LC inlet, outlet and center water samples were used to model (differential equation) the input and loss of phosphorus in LC and determine whether an equilibrium point exists. GCM analysis classified LC as a eutrophic wetland using the International standard and hypereutrophic using the Chinese standard.&#x0D; Results: Trophic state classification did not vary with use of consolidated bottom substrate versus flocculence samples. The differential equation model showed that SRP and TP levels within LC were higher than levels of SRP and TP entering LC, which could be caused by a nutrient recycling process within LC that may predict failure of remediation efforts. An equilibrium point was found at the eutrophic level, which means that even if there is a reduction in phosphorus input, there will not be a change in LC’s eutrophic state.&#x0D; Conclusions: Chinese trophic standard indicated LC was in a hypertrophic state. Similar results were found using the international standard. The differential equation model showed that LC is irreversible.

Positive and negative feedback loops in nutrient phytoplankton interactions related to climate dynamics factors in a shallow temperate estuary (Vistula Lagoon, southern Baltic)

Abstract This study aims to demonstrate that factors associated with climate dynamics, such as temperature and wind, affect the ecosystem of the shallow Vistula Lagoon in the southern Baltic and cause nutrient forms phytoplankton interactions: the growth of biomass and constraints of it. This occurs through a network of direct and indirect relationships between environmental and phytoplankton factors, including interactions of positive and negative feedback loops. Path analysis supported by structural equation modeling (SEM) was used to test hypotheses regarding the impact of climate factors on algal assemblages. Increased phytoplankton biomass was affected directly by water temperature and salinity, while the wind speed effect was indirect as it resulted in increased concentrations of suspended solids (SS) in the water column. Simultaneously, the concentration of SS in the water was positively correlated with particulate organic carbon (POC), particulate nitrogen (PN), and particulate phosphorus (PP), and was negatively correlated with the total nitrogen to phosphorus (N:P) ratio. Particulate forms of C, N, and phosphorus (P), concentrations of soluble reactive phosphorus (SRP) and nitrate and nitrite nitrogen (NO3-N + NO2-N), and ratios of the total N:P and DIN:SRP, all indirectly effected Cyanobacteria C concentrations. These processes influence other phytoplankton groups (Chlorophyta, Bacillariophyceae and the picophytoplankton fraction). Increased levels of SRP associated with organic matter (POC), which stemmed from reduced DIN:SRP ratios, contributed to increased Cyanoprokaryota and picophytoplankton C concentrations, which created a positive feedback loop. However, a simultaneous reduction in the total N:P ratio could have inhibited increases in the biomass of these assemblages by limiting N, which likely formed a negative feedback loop. The study indicates that the nutrients-phytoplankton feedback loop phenomenon can intensify eutrophication in a temperate lagoon, including increases of the biomass of Cyanobacteria and picophytoplankton. However, it can also constrain this increase.

Algal Growth Potential of Microcystis aeruginosa from Reclaimed Water.

Algal growth potential (AGP) of the cyanobacterium Microcystis aeruginosa (M. aeruginosa, NIES-298) using reclaimed water from various wastewater reclamation pilot plants was investigated to evaluate the feasibility of the reclaimed water usage for recreational purposes. After completing the coagulation and ultrafiltration processes, the concentrations of most contaminants in the reclaimed water were lower than the reuse guidelines for recreational water. However, M. aeruginosa successfully adapted to low levels of soluble reactive phosphorus (PO(3-)(4)) concentrations. The AGP values of M. aeruginosa decreased with the progression of treatment processes, and with the increases in the dilution volume. Also, both the AGP and chlorophyll-a values can be estimated a priori without conducting the AGP tests. Therefore, aquatic ecosystems in locations prone to environmental conditions favorable for the growth of M. aeruginosa require more rigorous nutrient management plans (e.g., reverse osmosis and dilution with clean water resources) to reduce the nutrient availability.

Calculating discharge of phosphorus and nitrogen with groundwater base flow to a small urban stream reach

Summary Elevated levels of nutrients, especially phosphorus, in urban streams can lead to eutrophication and general degradation of stream water quality. Contributions of phosphorus from groundwater have typically been assumed minor, though elevated concentrations have been associated with riparian areas and urban settings. The objective of this study was to investigate the importance of groundwater as a pathway for phosphorus and nitrogen input to a gaining urban stream. The stream at the 28-m study reach was 3–5 m wide and straight, flowing generally eastward, with a relatively smooth bottom of predominantly sand, with some areas of finer sediments and a few boulders. Temperature-based methods were used to estimate the groundwater flux distribution. Detailed concentration distributions in discharging groundwater were mapped using in-stream piezometers and diffusion-based peepers, and showed elevated levels of soluble reactive phosphorus (SRP) and ammonium compared to the stream (while nitrate levels were lower), especially along the south bank, where groundwater fluxes were lower and geochemically reducing conditions dominated. Field evidence suggests the ammonium may originate from nearby landfills, but that local sediments likely contribute the SRP. Ammonium and SRP mass discharges with groundwater were then estimated as the product of the respective concentration distributions and the groundwater flux distribution. These were determined as approximately 9 and 200 g d−1 for SRP and ammonium, respectively, which compares to stream mass discharges over the observed range of base flows of 20–1100 and 270–7600 g d−1, respectively. This suggests that groundwater from this small reach, and any similar areas along Dyment’s Creek, has the potential to contribute substantially to the stream nutrient concentrations.

The effect of a flood pulse on the water column of western Lake Superior, USA

On June 19 and 20, 2012, western Lake Superior was impacted by a “mega-rain event” that raised lake levels by 8 to 10cm. Within the flood plume on June 21, 2012, total suspended solids, total phosphorus, and soluble reactive phosphorus concentrations were elevated, with measurements of 87mg/L, >100μg/L, and 5.8μg/L, respectively. Despite the initially high phosphorus loadings, little impact was seen on water column particulate chlorophyll content, which remained in the range 0.7–1.9μg/L, in the weeks to months following the flood. Both total phosphorus and soluble reactive phosphorus levels tracked those of total suspended solids, returning to background levels within two weeks. However, the availability of photosynthetically available radiation (PAR) was impacted for a month after the flood event, due mainly to colored dissolved organic matter that remained in the surface layer of the stratified lake water column. It appears that the mismatch in timing of nutrient and light availability acted as a check on phytoplankton biomass production in the flood-impacted portion of the lake.

Beyond hypoxia: Occurrence and characteristics of black blooms due to the decomposition of the submerged plant Potamogeton crispus in a shallow lake

Organic matter-induced black blooms (hypoxia and an offensive odor) are a serious ecosystem disasters that have occurred in some large eutrophic shallow lakes in China. In this study, we investigated two separate black blooms that were induced by Potamogeton crispus in Lake Taihu, China. The main physical and chemical characteristics, including color- and odor-related substances, of the black blooms were analyzed. The black blooms were characterized by low dissolved oxygen concentration (close to 0 mg/L), low oxidation-reduction potential, and relatively low pH of overlying water. Notably higher Fe2+ and ΣS2− were found in the black-bloom waters than in waters not affected by black blooms. The black color of the water may be attributable to the high concentration of these elements, as black FeS was considered to be the main substance causing the black color of blooms in freshwater lakes. Volatile organic sulfur compounds, including dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, were very abundant in the black-bloom waters. The massive anoxic degradation of dead Potamogeton crispus plants released dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide, which were the main odor-causing compounds in the black blooms. The black blooms also induced an increase in ammonium nitrogen and soluble reactive phosphorus levels in the overlying waters. This extreme phenomenon not only heavily influenced the original lake ecosystem but also greatly changed the cycling of Fe, S, and nutrients in the water column.

Ecomorphological variability of Arthrospira fusiformis (Cyanoprokaryota) in African soda lakes.

The filamentous spirally coiled cyanoprokaryote Arthrospira fusiformis is found in extremely high densities in tropical soda lakes acting as driving force of the food web. We studied pronounced temporal morphological changes of Arthrospira in Kenyan soda lakes, Nakuru and Bogoria, and identified underlying key factors. Cell (diameter and height) and filament (height of coil, coil diameter, and number) dimensions were measured from weekly samples collected over a period of 16 months. In both lakes, medium-sized cells and large, widely coiled filaments prevailed most. Percentage of large, widely coiled filaments was promoted by elevated levels of soluble reactive phosphorus, wind speed, temperature and conductivity and the opposite for small filaments. Large, narrow-coiled filaments were associated with an increase in mainly Arthrospira-grazing zooplankton and cyanophage infections. Widely coiled spirals were promoted by increased turbulences. Based on fluorescence measurements, we found widely coiled filaments representing high vitality. From this study we were able to demonstrate for the first time morphological patterns of Arthrospira in nature. Arthrospira morphotypes are suitable for indicating the biological status in soda lakes as they are subjective and therefore reflective of what is happening in its habitat. Additionally, this outcome might be also of interest for commercial ′Spirulina′ farms in enhancing high-quality production.

Effects of temperature, algae biomass and ambient nutrient on the absorption of dissolved nitrogen and phosphate by Rhodophyte Gracilaria asiatica

Gracilaria asiatica, being highly efficient in nutrient absorption, is cultivated in sea cucumber ponds to remove nutrients such as nitrogen and phosphate. It was cultured in a laboratory simulating field conditions, and its nutrient absorption was measured to evaluate effects of environmental conditions. Ammonia nitrogen (AN), nitrate nitrogen (NN), total inorganic nitrogen (TIN), and soluble reactive phosphorus (SRP) uptake rate and removal efficiency were determined in a 4×2 factorial design experiment in water temperatures (T) at 15°C and 25°C, algae biomass (AB) at 0.5 g/L and 1.0 g/L, total inorganic nitrogen (TIN) at 30 μmol/L and 60 μmol/L, and soluble reactive phosphorus (SRP) at 3 and 6 μmol/L. AB and ambient TIN or SRP levels significantly affected uptake rate and removal efficiency of AN, NN, TIN, and SRP ( P< 0.001). G. asiatica in AB of 0.5 g/L showed higher uptake rate and lower removal efficiency relative to that with AB of 1.0 g/L. Nitrogen and phosphorus uptake rate rose with increasing ambient nutrient concentrations; nutrient removal efficiency decreased at higher environmental nutrient concentrations. The algae preferred to absorb AN to NN. Uptake rates of AN, NN, and SRP were significantly affected by temperature (P < 0.001); uptake rate was higher for the 25°C group than for the 15°C group at the initial experiment stage. Only the removal efficiency of AN and SRP showed a significant difference between the two temperature groups (P< 0.01). The four factors had significant interactive effects on absorption of N and P, implying that G. asiatica has great bioremedial potential in sea cucumber culture ponds.

Water quality status and phytoplankton composition in Soetendalvlei, Voëlvlei and Waskraalsvlei, three shallow wetlands on the Agulhas Plain, South Africa

Three wetlands on the Agulhas Plain, for which no limnological information was available, were investigated in order to provide baseline data on their present water quality and phytoplankton community structure. Physicochemical variables were assessed and phytoplankton biomass and community analyses were conducted seasonally in 2007. The water in all wetlands was well mixed with no thermal stratification at the time of sampling. Soluble reactive phosphorus levels corresponded to the eutrophic to hypertrophic category. Only Voëlvlei showed very high microalgal chlorophyll a levels (>400 μg l–1) due to the dominance of cyanobacteria. In the other wetlands, flagellates, chlorophytes and diatoms were the main microalgal groups. A high rainfall event in July–August 2007 considerably altered the phytoplankton community structure in Voëlvlei when cyanobacteria were completely replaced by chlorophytes. During August and November 2007 phytoplankton biomass was low in all the wetlands, and eutrophication signs were observed only in Voëlvlei. However, dense stands of both submerged and emergent macrophytes were present in two of the wetlands, the decomposition of which could lead to water quality changes. Voëlvlei had only large stands of emergent macrophytes (Phragmites and Schoenoplectus).

A multivariate analysis of covariance to determine the effects of near-stream best management practices on nitrogen and phosphorus concentrations on a dairy farm in the New York Conservation Effects Assessment Project watershed

Near-stream best management practices (BMPs), such as exclusionary fencing or cattle crossings, are often recommended to improve water quality, but quantification of their impacts is limited. Surface and subsurface processes in these near-stream areas impact the contribution of nitrogen and phosphorus to watercourses and the effectiveness of near-stream BMPs. To test the impact of the near-stream BMPs, groundwater samples from 30 piezometers and streamwater samples along two adjacent creeks (one control and one with BMP treatment) were collected over a three-year period before and after installation of exclusionary fencing with a cattle crossing in the Catskill Mountains of New York State. Samples were analyzed for nitrate nitrogen (NO₃⁻-N), soluble reactive phosphorus (SRP), dissolved oxygen, and dissolved organic carbon. Analysis results and other ancillary variables (rainfall and groundwater table depth) were incorporated into a multivariate statistical model to evaluate the impact of the BMPs on the concentrations of NO₃⁻-N and SRP in the treatment creek. Results of the analysis indicate that the installation of the near-stream BMPs resulted in a 27% yearly (34% during the growing season) reduction in treatment creek SRP concentrations, while there was little impact on NO₃⁻-N concentrations. Incorporating the SRP concentrations measured in a nearby control creek and controlling for the effects of groundwater SRP levels and groundwater hydrology (water table height) had a significant effect on the overall analytical model performance. These results indicate that protecting near-stream areas from potentially pollution-causing practices can be an important means of controlling phosphorus levels in water bodies.

A mass balance evaluation of the ecological significance of historical nitrogen fluxes in Lake Kinneret

Lake Kinneret (LK) is a monomictic lake that has undergone significant biological and chemical changes over the last three decades of the twentieth century. The transition between the 1970s and the 1980s attracted a lot of scientific attention as it was marked by significant changes in the ecology of the lake. In the early 1980s, phytoplankton biomass increased, apparently in response to an increase in the external soluble reactive phosphorus (SRP) load. This period was marked by a rise in hypolimnetic levels of ammonium (NH4) and SRP as well as surface water dissolved oxygen (DO) and pH. Cconcomitantly, in surface waters in winter levels of NH4 increased and NO3 decreased. In this study interrelationships amongst these observations were examined with a mass balance modelling approach, including simulation of individual nutrient sources and sinks, focusing on nitrogen fluxes in winter. The step-like rise in phytoplankton biomass in 1981 may have been triggered by the increase in winter external loads of SRP, as P is likely to be the growth-limiting nutrient during this season. The additional P load led to a sequence of changes including greater summer phytoplankton biomass, followed by enhanced sedimentation of organic matter. Furthermore, higher organic matter mineralization fluxes within the hypolimnion resulted in elevated levels of NH4 and SRP in this layer through the 1980s, with a feedback to productivity in the trophogenic zone following seasonal destratification in early winter. In an apparent transition period (late 1970s to early 1980s), an increase in the modelled rate of nitrate (NO3) production occurred via nitrification together with increased uptake of the additional nitrate by phytoplankton. These results are consistent with increased phytoplankton abundance and elevated levels of surface water NH4 and DO during this period. Through this period the increase in phytoplankton uptake of NO3 predominated over the increase in nitrification, and NO3 concentrations in the 1980s were reduced compared with the previous decade, with increased partitioning of N in biomass and NH4.

Relationships between environmental factors, periphyton biomass and nutrient content in Garças Reservoir, a hypereutrophic tropical reservoir in southeastern Brazil

This study focused on evaluating the factors related to seasonal variations of periphyton biomass and nutrient content (N, P) in Garcas Reservoir, a tropical, shallow hypereutrophic tropical reservoir in southeastern Brazil that exhibits a permanent cyanobacteria bloom. Artificial substrata were placed in the subsurface water (20 cm) of the lake on a monthly basis (incubation time of 28 days) over a 1-year period. Two limnological periods were characterized, including: (i) a period of decreased water clarity, higher levels of soluble reactive phosphorus and higher phytoplankton biomass; and (ii) a period of relatively higher water clarity (as measured by Secchi depth), higher nitrate concentration and lower phytoplankton biomass. The periphyton chlorophyll-a levels were lower during the first period, being negatively correlated with phytoplankton biomass. The results of this study suggest that during the period of decreased water clarity, periphyton was primarily light-limited. In contrast, the periphyton biomass was higher during the second period, regardless of P limitation of periphyton growth. Rehabilitation of this highly degraded tropical reservoir must consider the light regime, which is controlled by phytoplankton abundance. Thus, a reduction in the P loading to the lake should be considered to suppress its cyanobacterial blooms, thereby improving conditions for submerged macrophytes and the re-establishment of periphyton.

Great Lakes Cladophora in the 21st century: same algae—different ecosystem

Nuisance growth of the attached, green alga Cladophora was considered to have been abated by phosphorus management programs mandated under the Great Lakes Water Quality Agreement. The apparent resurgence of nuisance growth in Lakes Erie, Michigan and Ontario has been linked conceptually to ecosystem alterations engineered by invasive dreissenid mussels ( Dreissena polymorpha and D reissena bugensis). Here, we apply contemporary modeling tools and historical water quality data sets in quantifying the impact of long-term changes in phosphorus loading and dreissenid-mediated changes in water clarity on the distribution and production of Cladophora. It is concluded that reductions in phosphorus loading in the pre-dreissenid period achieved the desired effect, as model simulations were consistent with the biomass declines reported from the early 1970s to the early 1980s. These declines were, however, largely offset by dreissenid-driven changes in water clarity that extended the depth of colonization by Cladophora, increasing total production. We were not able to isolate and quantify the significance of dreissenid mediation of phosphorus cycling using the historical database. Phosphorus management remains the appropriate mechanism for reducing nuisance levels of Cladophora growth. The development of action plans will require an improved understanding of nearshore phosphorus dynamics such as might be obtained through regular monitoring of soluble reactive phosphorus levels, internal phosphorus content and Cladophora biomass in impacted nearshore regions of the Great Lakes.