Headwater Research Articles

Effect of Seasonality and Associated Environmental Drivers on Macroinvertebrate Assemblages in Neotropical Coastal Headwater Streams

ABSTRACTComprehensive research into the environmental factors that affect the spatial and temporal variability of benthic macroinvertebrate communities in the headwater coastal streams of Ecuador is limited. Therefore, a study was carried out in four headwater coastal streams to address this gap. This study lasted for 2 years and included two surveys in summer and two in winter. The spatial and temporal variation of community metrics (abundance, richness, and diversity), functional feeding groups, and environmental factors were analyzed. A total of 47 genera from 33 families and 12 orders were collected, 29 of which were new records for the studied region. Seventy‐nine percent of the total number of macroinvertebrates collected belonged to three orders of insects: hemipterans, ephemeropterans and coleopterans. The most abundant non‐insect was the amphipod Hyalella. In seasonal terms, the populations of odonates, hemipterans, and coleopterans decreased in winter, whereas those of amphipods, trichopterans, ephemeropterans, and dipterans increased. The dominant functional feeding group consisted of predators, with the heteropterans Rhagovelia and Husseyella being the most abundant genera across all streams. Populations of predators and scrapers decreased in winter, whereas those of shredders and collectors increased. The results showed significant differences among the macroinvertebrate metrics obtained for each stream and season. The abiotic PCA ordination and biotic NMDS ordination of macroinvertebrate assemblages were consistent. The BEST routine inferred that the environmental variables that best explained assemblage patterns were phosphate concentration and stream width, although dissolved oxygen, water temperature, and current velocity were also important explanatory variables. In conclusion, seasons had a major influence on the macroinvertebrate assemblages of neotropical coastal headwater streams. During summer (the dry season), environmental stability supported higher richness and diversity, whereas in winter (the rainy season), hydrologic perturbation disrupted and altered the structure and composition of the macroinvertebrate community.

Relative contributions of climate and grazing to forage supply in the Yellow River source area.

Grassland ecosystems, critical for ecosystem services like forage supply, face threats from climate change and grazing pressure. This study investigates the spatiotemporal dynamics of forage supply and grazing intensity in the Yellow River Source Area (YRSA) from 2000 to 2020, focusing on the relative contributions of climate factors and grazing. Our result revealed that forage supply exhibited a southeast-to-northwest decline and increased slightly overall, with variability among grassland types. Using a Livestock Carrying Pressure Index (LCPI), which incorporating seasonal grazing practices and supplementary feeding, we found that grazing intensity showed spatial heterogeneity, with moderate grazing pressure (1.5<LCPI<2.5) to heavy grazing pressure (LCPI>2.5) in the northeast, and understocked (LCPI<0.9) in central and southern regions. Precipitation was identified as the dominant factor positively influencing forage supply in northern and western YRSA, while grazing intensity negatively affected forage supply in most area. We further quantified the relative contributions of these factors, revealing that precipitation played the most significant role in the north and west, while grazing intensity was the primary driver in specific central and southern areas. Grazing intensity dominates 42.4% of grasslands, surpassing precipitation (40.7%) and temperature (16.9%). These findings underscore the need for climate-adaptive grazing management strategies to optimize forage production and safeguard the YRSA's ecological functions.

Assessing riparian functioning condition for improved ecosystem services: A case study of the Back Creek watershed (Virginia, USA).

Riparian functioning condition refers to a rating and description of the current ecological status of a reach of a riparian ecosystem in consideration of its potential hydrology, vegetation, and geomorphology. Reach rating options are Proper Functioning Condition (PFC), Functional-At-Risk (FAR), Non-Functional, and apparent or monitored trends. We assessed the functioning condition of flowing riverbank areas of Back Creek located in Virginia (USA) following a PFC protocol developed by the U.S. Department of the Interior and the U.S. Department of Agriculture. The PFC protocol involves 17 qualitative assessment items that address three categories of attributes (hydrology, vegetation, and geomorphology); each is answered as "yes", "no," or "not applicable" with an explanation. We discussed key PFC items driving stream water quality contextualizing the previously modeled riparian buffer zones and ecosystem services tradeoffs in the Back Creek watershed published by U.S. Environmental Protection Agency. Using the remote sensing data in the Geographic Information System, we delineated and characterized 26 Back Creek reaches of 41.1km length. We also analyzed the 38-year (1981-2018) daily datasets of the precipitation, surface runoff, temperature, soil moisture pattern, and vegetation types for the watershed. Then, we conducted the PFC assessments using field reconnaissance of 10 reaches, 19.3km of the Back Creek. The field assessments concluded that 52% of the assessed length of Back Creek was in PFC, attributed to diverse vegetation, maintained channel characteristics, floodplain accessibility (where appropriate), and balanced water and sediment loading supplied by individual headwater streams to the Back Creek. 48% of the assessed length was in FAR condition due to land use changes and urban road network. This study provides an exemplar of nonpoint source (diffused pollution generated by land runoff) methodology for identifying key riparian functioning issues and assessing effectiveness of the non-point source best management practice programs.

Keystone bacterial groups dominate Escherichia coli O157:H7 survival in long-term reclaimed water headwater stream.

Escherichia coli (E. coli) O157:H7 is a highly pathogenic zoonotic bacterium, with water serving as a key medium for its environmental transmission. However, the survival characteristics of E. coli O157:H7 in reclaimed water environments remain poorly understood, which has, to some extent, hindered the development of water reuse technologies. This study examined the survival dynamics of E. coli O157:H7 in a long-term reclaimed water headwater stream through inoculation experiments and identified its main drivers. The results showed that the survival time of E. coli O157:H7 was the longest in the headwater upstream (up to 62 days), gradually decreased as it flowed downstream. Among physicochemical factors, chloride ion, potential of hydrogen, and electrical conductivity were the main factors affecting the survival of E. coli O157:H7. The microbial diversity shown by the alpha diversity index had no significant impact on the E. coli O157:H7 survival. Meanwhile, certain keystone bacterial groups, such as Polynucleobacter, Roseomonas, and Luteolibacter, which are primarily involved in the decomposition of organic matter, suppressed E. coli O157:H7 survival in this stream, while Nitrospira, Dechloromonas, and Sphingomonas promoted the survival of E. coli O157:H7. Overall, the biotic factors have a more direct impact on the E. coli O157:H7 survival compared to abiotic factors in the reclaimed water-replenished stream and deserve more attention. Our research revealed higher biological risks in the upstream sections of the long-term reclaimed water headwater stream, which helped deepen our understanding of pathogen survival in water environments and enhancing our awareness of the biological safety of reclaimed water in ecological replenishment processes.

Benthic bacterial communities are shaped by browning in boreal headwater streams

Benthic bacterial communities are shaped by browning in boreal headwater streams

Longitudinal and temporal variation in fish assemblage structure along lowland prairie Neotropical streams and relationships with environmental variables

The structure of fish assemblages in lotic systems usually varies from headwaters to the mouth, related to geomorphological and physicochemical changes. We evaluated the main processes that structure the fish assemblages on spatial, seasonal, and decadal (2009-2010; 2019-2020) scales and relationships with environmental variables in two low-impacted Neotropical Pampean streams tributaries to the Río de la Plata estuary (RdlP). Environmental variables related to the longitudinal variation in the fish assemblage were depth, macrophyte cover, and altitude, showing higher values in the headwater streams compared to downstreams. Species richness increased towards lower stream sectors due to the migration of riverine species from the RdlP. Beta diversity partitioning analysis showed that the greatest proportion of variability was explained by the turnover component in both the longitudinal and seasonal analyses. The headwater streams showed a more stable composition, consisting of species of the order Characiformes associated with aquatic macrophytes, while the downstream streams recorded greater variability due to the entry of migrant Siluriformes from the RdlP, highlighting the essential ecological function of Pampean streams for RldP fish assemblages. The decadal comparison showed that the longitudinal structure is persistent in the long term regardless of the study period. Therefore, the consistent pattern of longitudinal variation in fish assemblages and its explanatory variables have applicability in the conservation and biomonitoring of lowland streams, serving as reference for recovery efforts.

Influence of hydrological environments on the spawning behavior of landlocked amago salmon in the headwater streams of the Tendani River, Japan

Influence of hydrological environments on the spawning behavior of landlocked amago salmon in the headwater streams of the Tendani River, Japan

Characterizing Stream Condition with Benthic Macroinvertebrates in Southeastern Minnesota, USA: Agriculture, Channelization, and Karst Geology Impact Lotic Habitats and Communities.

Prior to implementing watershed-wide projects to reduce the impacts of agriculture on regional streams and rivers, stream habitats and benthic aquatic macroinvertebrate communities were assessed at 15 sites on the South Branch Root River and its major tributaries in southeastern Minnesota, USA. Triplicate kick-net samples were collected from each site during three time periods (1998, 1999, 2006/2008) and stream habitats were inventoried within 150 m long sections at each site. In total, 26,760 invertebrates representing 84 taxa were collected and used to rate stream sites using a regional multi-metric benthic index of biotic integrity (BIBI). BIBI scores were significantly correlated with total invertebrate taxa richness. BIBI ratings improved from poor and very poor at headwater sites in channelized stream sections draining agricultural lands to fair to good to excellent in downstream sections flowing through natural channels in largely forested lands. Fifty percent of samples rated stream sites as poor or very poor. Over 85% of stream habitat assessments indicated the presence of fair to good habitats, although stream sites were relatively wide and shallow and dominated by fine sediments that also embedded coarser substrates. BIBI metrics and scores were strongly positively correlated with pool area, riffle spacing-to-stream width ratios, and silt-free substrate, and negatively correlated with width-to-depth ratios. Most stream sites had few Ephemeroptera, Plecoptera, Trichoptera, and Diptera taxa and too few intolerant taxa. It is expected that benthic invertebrate communities should improve as more riparian buffers are added along all streams. However, on-going channel maintenance activities in headwater stream sections, mandated to encourage drainage of adjacent agricultural fields, will continue to negatively impact headwater habitats and biotic communities.

Analysis of the complex correlations between land use and water quality using the PLS-SEM method combined with fluorescence fingerprinting data.

Accurate analysis of surface water pollution mechanisms is critical for effective environmental restoration and protection. However, evaluation methods for small watersheds with dense populations and complex pollution sources remain limited. This study integrates partial least squares structural equation modeling (PLS-SEM) with fluorescence fingerprinting data from excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) to investigate nutrient sources in rivers of southeastern China. The findings reveal that land use intensity (LUI) significantly influences pollutant concentrations, but the presence of outliers underscores complex pollution mechanisms. Using EEM-PARAFAC components as mediators, the C5 component, representing sewage-derived substances, was identified as a key driver, fully mediating nitrogen (β=0.953, p<0.001, VAF=117.5%) and phosphorus (β=0.921, p<0.001, VAF=113.2%) levels. In contrast, agricultural non-point sources (C1 and C2: β=-0.270, p>0.05) had negligible direct effects on nutrient concentrations, emphasizing the need to prioritize domestic sewage control. Additionally, components C1 and C2 exerted strong direct effects on dissolved organic carbon (β=0.495, p<0.001), surpassing the influence of sewage (β=0.380, p<0.001). These results demonstrate that the combined use of PLS-SEM and EEM-PARAFAC is a robust approach for identifying pollution sources in data-limited small watersheds, supporting cost-effective aquatic environmental restoration strategies.

Multidecadal trends in brown trout populations in France reveal a decline in adult abundance concomitant with environmental changes

Most studies of brown trout ( Salmo trutta) populations in headwater streams have focused on the year-to-year variability in recruitment and survival, but only few analyzed long-term trends in trout densities, under both control and regulated flow conditions. Here, we conducted trend analyses of brown trout age class densities on 36 stream reaches over the 1990–2020 period, including reaches located in a bypassed section. We also investigated long-term trends in a panel of key environmental variables (water temperature, stream flow, current velocity, and habitat suitability). We found that annual water temperatures significantly increased by a median of +0.21 °C per decade. Analyses of stream flow revealed only a few significant trends, including a general increase in median values in spring and a general decrease in fall. A significant general decline in adult trout densities was observed, although disparities between geographic areas were highlighted. This decline is likely due to multifactorial effects, including possible interacting factors. Our results highlight the need to maintain and extend long-term monitoring of trout populations, which should be combined with extensive environmental monitoring.

Hysteretic response of suspended‐sediment in wildfire affected watersheds of the Pacific Northwest and Southern Rocky Mountains

AbstractWildfires can have a profound impact on hydrosedimentary interactions, or the relationship between sediment and runoff, in forested headwater streams. Quantification of sediment‐runoff dynamics at the event scale is integral for understanding source areas and transport of suspended‐sediment through a watershed following wildfire. Here we used high‐frequency turbidity and stream discharge data, coupled with discrete suspended‐sediment measurements, in burned and unburned watersheds in the Southern Rocky Mountains and the western Cascades Range to evaluate the response of fine‐grained (clay‐ and silt‐sized particles) suspended‐sediment. Hysteresis analysis was conducted on estimated suspended‐sediment concentrations (using turbidity as a proxy) and streamflow through measurement of the difference in sediment concentration on the rising and falling limbs of the event hydrograph. All burned watersheds exhibited elevated fine suspended‐sediment concentrations relative to concentrations found in pre‐fire conditions. Changes to hysteretic response vary and may depend on a watershed's sediment connectivity limitations. Results suggest a watershed's inherent hillslope‐to‐channel (or lateral) connectivity is the primary factor controlling the relative magnitude of event‐driven fine sediment fluxes in watersheds affected by wildfire. While wildfire did promote lateral connectivity through activation of hillslope sources, snowmelt, precipitation characteristics and antecedent conditions were more important drivers of hysteretic response than wildfire. For watersheds influenced by annual snowpack, we identified a predominantly clockwise hysteretic response during snowmelt and counterclockwise events during the late spring and summer months. There were also proportionally more counterclockwise events after wildfire in watersheds with high sediment connectivity. Results suggest contrasting wildfire‐related sediment risk potential. Rivers in burned watersheds with high sediment connectivity may pose a higher risk to receiving waterbodies, such as larger tributaries or reservoirs, while rivers with low sediment connectivity may experience long‐term sediment‐related risk within the watershed above the outlet.

A Surface Freeze-Thaw Cycle Detecting Framework Based on Passive Microwave Data for the Alpine Zone: A Case Study of Three River Source Region in the Qinghai-Tibetan Plateau

A Surface Freeze-Thaw Cycle Detecting Framework Based on Passive Microwave Data for the Alpine Zone: A Case Study of Three River Source Region in the Qinghai-Tibetan Plateau

English

Abstract Crayfishes in the Genera Procambarus, Pacifastacus, Faxonius, Cherax, and Cambarellus were evaluated for their potential impacts and overall invasion risk in Ontario. Of the ten species evaluated, six have been found to have potential high impact. Crayfishes in the genus Procambarus pose the greatest risk as they have the greatest potential for negative impacts on native species and habitats. Three of the species have already recently been detected in Ontario. A single population of P. virginalis in the city of Burlington is the first of this species in Canada and North America. Procambarus acutus appears to be well-established in both the Lake Erie and Lake Huron watersheds while P. clarkii has also been most recently reported in Southern Ontario. The invasive Faxonius rusticus is well established and still expanding in Ontario and has displaced native crayfishes in large parts of the province while F. limosus appears poised to expand into Ontario. It is recommended that a different set of regulations be drafted and applied to all introduced species in Ontario, including the already present species (F. rusticus, F. obscurus, P. acutus, and P. virginalis) as well as any future introduced species of crayfish. Education and outreach for anglers, naturalists, and the general public is recommended as an effective way of preventing the introduction and spread of invasive crayfishes. For crayfish which are already well established or recently detected in Ontario, management efforts should focus on containment of any further spread. Citizen science contributions to on-line databases, such as iNaturalist and EDDMapS, are also crucial in tracking introduced species in the province. Priority should be given to safeguarding remnant populations of native crayfishes, especially in areas dominated by introduced species. Headwaters of streams and rivers, as well as isolated lakes and small wetlands, are well suited for this type of conservation management.

Optimization of Grassland Carrying Capacity with Grass Quality Indicators Through GF5B Hyperspectral Images

The accurate estimation of grassland carrying capacity (GCC) in the alpine grasslands of the Changjiang River source region is crucial for managing livestock loads and ensuring ecological security on the Qinghai-Tibetan Plateau. Previous remote sensing methods have predominantly focused on yield indicators, often neglecting quality indicators, which hampers precise GCC estimation. Here, we collected 25 samples from the Dangqu basin, analyzing various grass parameters including yield, crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF). Then, we developed models to optimize GCC using quality indicators derived from GF5B images, assessing performance through Pearson correlation coefficient (R2), root mean square error (RMSE), and relative root mean square error (rRMSE). Results were found to show an average yield of 61.26 g/m2, with CP, ADF, and NDF ranging from 5.81% to 18.75%, 45.47% to 58.80%, and 27.50% to 31.81%, respectively. Spectra in the near-infrared range, such as 1918 nm, and spectral indices improved the accuracy of the hyperspectral inversion of grass parameters. The GCC increased from 0.51 SU·hm−2 to 0.63 SU·hm−2 post-optimization, showing an increasing trend from northwest to southeast. This study enhances GCC estimation accuracy, aiding in reasonable livestock management and effective ecological preservation.

Soil Organic Carbon Storage and Stratification in Land Use Types in the Source Area of the Tarim River Basin

Accurate analysis of soil organic carbon (SOC) under different land uses in ecologically fragile arid zones is essential for effective regulatory measures and improvement of ecological quality. This study selected the ecologically fragile Tarim River source area as an example, aiming to quantitatively assess the SOC content, storage, carbon sequestration potential, and stratification ratio (SR) of different ecological land use types. Soil depths from 0–50 cm were determined and analyzed using the K2Cr2O7-H2SO4 oxidation method, the equivalent soil mass method and mathematical statistics. Forest, shrubland, and grassland ecological land types were included. The results show the following: (1) Both SOC content and storage showed a decrease with increasing soil depth. The total SOC content and storage sequence from high to low were natural forest, grassland, and shrubland. (2) There are variations in the SOC sequestration potential among the different ecological land types and shrubland (40.64 Mg C ha−1) &gt; grassland (37.69 Mg C ha−1). (3) The SRs of the SOC in the forest were significantly greater than those in the shrubland and grassland. The different ecological land types had significant impacts on SR2, SR3, and SR4. SR2 could serve as a reliable index for assessing the impact of management practices on soil quality. The study area has a high potential for soil carbon sequestration in the future under these ecological conservation and management measures.

Jute-Copper Nanocomposite Embedded PSf Membrane for Sustainable and Efficient Heavy Metal Removal from Water Sources.

Numerous corporations have overlooked environmental regulations concerning wastewater treatment, leading to a worldwide issue regarding hazardous pollutant discharge, particularly dyes and heavy metal ions, into river sources. Various industries, with water, energy, and biological sectors, actively employ membranes. Membranes capable of showing flux, metal and dye sorption, and catalysis have been developed and are extensively used by functionalizing the pores of ultrafiltration, microfiltration, and nanofiltration membranes with responsive properties. The enhancement of synthetic membrane performance can be achieved by developing new polymers or modifying the surface of existing polymers. In this study, high porosity and large internal pore volume polysulfone (PSf) membrane composites were produced on a laboratory scale by adjusting the polymer coagulation conditions during the phase inversion process, incorporating copper nanoparticles for antifouling properties, and utilizing pretreated natural jute fibers. A comprehensive characterization of the composites was conducted by using FTIR, XRD, XPS, ICP-MS, and SEM techniques. To calculate their possible uses in separation and purification methods, the performance of PSf-based membrane composites was evaluated in terms of heavy metal rejection rates (%) in water.

Monitoring Spatial-Temporal Variability of Vegetation Coverage and Its Influencing Factors in the Yellow River Source Region from 2000 to 2020

As a vital conservation area for water sources in the Yellow River Basin, understanding the spatial-temporal dynamics of vegetation coverage is crucial, along with the factors that affect it, to ensure ecological preservation and sustainable development of the Yellow River Source Region (YRSR). In this paper, we utilized Landsat surface reflectance data from 2000 to 2020 using de-clouding and masking methods implementing the Google Earth Engine (GEE) cloud platform. We investigated spatial-temporal changes in vegetation coverage by combining the maximum value composite (MVC), the dimidiate pixel model (DPM), the Theil–Sen median slope, and the Mann–Kendall test. The influencing factors on vegetation coverage were quantitatively analyzed using a geographic detector, and future tendencies in vegetation coverage were predicted utilizing the Future Land Use Simulation (FLUS) model. The outcomes suggested the following: (1) On the temporal scale, vegetation coverage exhibited a general upward trend between 2000 and 2020, with the YRSR showing a yearly growth rate of 0.23% (p &lt; 0.001). In comparison to 2000, the area designated as having extremely high vegetation coverage increased by 19.3% in 2020. (2) Spatially, the central and southeast regions have higher values of vegetation coverage, whereas the northwest has lower values. In the study area, 75.5% of the region demonstrated a significant improvement trend, primarily in Xinghai County, Zeku County, and Dari County in the south and the northern portion of the YRSR; conversely, a notable tendency of degradation was identified in 11.8% of the area, mostly in the southeastern areas of Qumalai County, Chenduo County, Shiqu County, and scattered areas in the southeastern region. (3) With an explanatory power of exceeding 45%, the three influencing factors that had the biggest effects on vegetation coverage were mean annual temperature, elevation, and mean annual precipitation. Mean annual precipitation has been shown to have a major impact on vegetation covering; the interconnections involving these factors have increased the explanatory power of vegetation coverage’s regional distribution. (4) Predictions for 2030 show that the vegetation coverage is trending upward in the YRSR, with a notable recovery trend in the northwestern region. This study supplies a theoretical foundation to formulate strategies to promote sustainable development and ecological environmental preservation in the YRSR.

Stream bryophytes promote “cryptic” productivity in highly oligotrophic headwaters

AbstractRecent observations document increased abundance of algae in the headwater streams of Hubbard Brook Experimental Forest (HBEF). It is possible that this “greening up” of HBEF streams may be due to climate change, with rising temperatures, altering terrestrial phenology, and shifting hydrologic regimes. Alternatively, stream “greening” could be from the slow recovery of stream chemistry after decades of acid rain, which has led to rising pH, declining concentrations of toxic Al3+, and low solute concentrations. Four years of weekly algal measurements on artificial moss and ceramic tiles, along with six nutrient enrichment experiments, revealed new insights about the interactions between these two autotrophs. We found that in protected weir ponds and in stream channels, algal biomass was higher on artificial moss substrates than on tiles—with this effect amplified in the stream channels. These results suggest that bryophytes can provide physical protection from flood scour or may trap nutrients to support algal growth. In stream channels, algal biomass was higher in well‐lit habitats and time periods indicating strong light limitation. We only measured nitrogen and phosphorus limitation of algal biomass in nutrient enrichment experiments conducted within weir ponds, with higher light availability and lower flow. By comparison, results from the remaining four instream experiments provided little evidence for nutrient limitation, with only one trial showing increased algal growth in response to nutrient addition. The most striking implication of our study is the role of bryophytes in providing refugia, and potentially nutrients, to algae in shaded and oligotrophic headwater streams.

Hydrochemical characteristics of water quality of the Bystrytsia River basin (Lviv region)

The article investigates the hydrochemical composition of water in the Bystrytsia River basin. The ratio of the main water ions was determined and it was found that along the flow the hydrochemical facies of water changes from HCO3-–Ca2+ to HCO3-–Ca2+–Mg2+. River water has an average mineralization, which increases from 391 mg/l to 463 mg/l. The reaction of the environment in the Bystrytsia River basin is mostly slightly alkaline (pH=8.15) and changes to neutral (pH=7.2) in the village of Hrushiv. Permanganate oxidation of river water in the village of Velyka Ozymyna is higher than in other areas and is associated with the presence of lowland peatlands in this area, which are a source of humic acids. A tendency for a gradual increase in phosphates P–PO43- from the river source to its mouth and sudden changes in the concentration of nitrates N–NO3- has been noted. The contamination coefficients of such biogenic elements are less than 1. Ammonium ions, nitrites and many heavy metals (Zn, Mn, Cu, Co, Ni, Pb) were not detected in the river water of the Bystrytsіa river basin. The water in the Bystrytsia River basin corresponds to class 1 according to the water pollution index (very clean, IW=0.02-0.16) and this indicator is 1.8 times lower than in the Dniester River. The increase in the water pollution index along the river is due to increases in the multiplicity of phosphates in the water. The ecological state of water in the Bystrytsia River basin using the complex indicator СPES was determined to be stable with features of instability (CPESmin=-0.61 and CPESav=0.87), instability was detected in the Novoshytska HPP reservoir, in the villages of Zalokot and Urizh. The negative complex indicator of the ecological state of water in these areas corresponds to the sanitary and toxicological indicators (CPES 3) and is due to the influence of magnesium ions, which dominate over Ca2+ ions in river water, form the HCO3- – Mg2+ or HCO3- – Mg2+ – Ca2+ hydrochemical facies and exceed the permissible content. A stable water state with features of instability has been established in the Dniester and Cherkhavka rivers. According to the IZV, the waters are very clean, but have increased mineralization (&gt;500 mg/l), higher hardness (5.8 and 4.7 mmol-eq/l), stronger acidity (pH=7.2 especially in the Dniester), higher permanganate oxidation (4.2 mg O/l mostly in the Dniester), higher concentration of Fe3+ ions (4.9 μg/ml mostly in the Dniester). The hydrochemical composition of the water is different: HCO3- – Ca2+ – Mg2+ in the Dniester and Ca2+– HCO3- – Na+ in the Cherkhavka. These analytical results would be useful for building a hydrological conceptual model that ensures better use of the natural water system in the Bystrytsia River basin. Key words: Bystrytsia River basin; main ions; biogenic components; chemical oxygen demand; water pollution index; water quality assessment by a complex indicator.

Patterns of nutrient limitation of algal productivity from headwaters to estuary

Studies of algal growth responses to nutrient availability at the catchment scale are sparse. Here we study algal nutrient responses in headwater streams, rivers, lakes and the estuary in a temperate, coastal catchment. Nutrient enhancement bioassays were used to determine phytoplankton and periphyton growth limitation by N and/or P availability. In addition, N and P concentrations and ratios in water were measured. In the headwaters, algae were most often limited by nitrogen (N) and N and phosphorus (P), while algae further downstream became progressively less nutrient limited. Unlike other sites in the catchment, phytoplankton in a lowland, headwater lake was almost always N-limited, indicating that local characteristics shifted nutrient availability and limitation status towards P saturation. Nutrient limitation state could be correctly inferred from dissolved inorganic nitrogen:P ratios at only four of the eight sites, highlighting the limited efficacy of nutrient ratios alone for inferring nutrient limitation status. Our results show that reduction of N and/or P concentrations to below growth-limiting thresholds could reduce algal productivity and biomass in the lower catchment, but not consistently because nutrient limitation status varied greatly at sites within the catchment. Our study adds to the growing literature indicating that drivers of eutrophication can be spatially and temporally variable, even within a single catchment.