Groundwater Inputs Research Articles

Surface-derived groundwater contamination in Gulu District, Uganda: Chemical and microbial tracers

Groundwater is consumed by over 2 billion people globally, though it can be impacted by microbial and chemical contamination in both rural and (peri-)urban areas. This issue is particularly pertinent in regions like East Africa, where rapid urbanisation has strained local infrastructure, including water and sanitation systems. We use selected tracers of human and animal waste to assess the quality of community drinking sources with regards to surface-derived groundwater inputs and to compare urban versus rural water quality, under the rapidly developing urban area of Gulu, Northern Uganda. Specifically, we examine bulk and fluorescent dissolved organic matter (DOM), microorganisms (total coliforms, E.coli) and inorganic tracers of anthropogenic waste (NO3−, SO42−, Cl/Br) from various sources: boreholes (12–76 m depth; n = 90), protected springs (n = 11) and municipal taps (n = 4). Our results show that NO3− and SO42− were elevated in groundwater sources in the Gulu city urban area and the Cl/Br ratio was elevated in springs, compared to concentrations in the more rural Aswa and Omoro County area (p < 0.05). Interestingly, human and animal waste indicators E.coli and Tryp:FA (the ratio of tryptophan-like to fulvic-like fluorescence) displayed no significant difference between rural and urban settings (p > 0.05), though total coliforms were significantly higher in rural boreholes (p < 0.05). The presence of a pollution source, pollution carrier and a breakdown of a sanitary barrier at the borehole, as spot-checked by a visual sanitary risk assessment, was significantly associated with groundwater E.coli abundances. Evidence suggests monitoring and mitigation should be improved for all water types in Gulu District to meet WHO and Uganda Standard guidelines for potable water. This study offers valuable insights for water management planning and risk assessment of community water sources particularly in the context of East Africa and similar settings.

Influence of submarine groundwater discharge on the nutrient dynamics of a fringing-reef lagoon

Study regionThis study investigates nutrient distribution and flux dynamics in a coral reef lagoon in Quintana Roo, Mexico, located on a permeable limestone coast of the Mesoamerican Barrier Reef System. Study FocusEmphasis is placed on submarine groundwater discharge (SGD) as a crucial contributor to nutrient pathways, including ammonium (NH4+), nitrate and nitrite (NOx-), hydrogen silicate (HSiO3-), hydrogen phosphate (HPO42-), and urea. Inputs vary with SGD magnitudes and sources and by proximity to active spring discharges. Groundwater multi-tracer analysis and multiple linear regression identify 226Ra as explaining NH4+ variability due to long-term groundwater processes, while 223Ra predicts NOx-, HSiO3-, and urea due to short-term inputs. No significant relationship was found between HPO42- and any radium isotope, indicating complex behavior in coastal karst aquifers. New hydrological insights for the regionThe findings highlight complex nutrient dynamics in coastal karst settings, with SGD-derived fluxes primarily consisting of dissolved inorganic nitrogen (DIN) and HSiO3-. Although lower in concentration, HPO42- and urea fluxes are significant compared to other karst environments. Radium isotopes distinguish between short-term and long-term, as well as new and recycled nutrient inputs. Groundwater inputs transport fresh nutrients to healthier reefs, whereas processed, recycled inputs were detected near degraded reefs. These insights are essential for understanding global nutrient cycles and coral health, particularly in the context of global change and anthropogenic disturbances affecting coral reef ecosystems.

Integrated water operations under climate change: Uluova Micro Basin example

ABSTRACT This study examines the impact of climate change on the Uluova Micro Basin, Turkey, employing an optimization model named ULUHEM across various water management and climate scenarios. With ULUHEM, the effects of different climate impact scenarios on agricultural water allocations, pumping costs, water scarcity, and scarcity costs were analyzed. The primary objective of this study is to identify gaps in demand within the current water supply infrastructure due to global warming and to develop adaptation strategies for basinwide water management operations. The research also emphasizes the importance of creating a basin-based hydroeconomic model that includes other surface water resources with a sustainable management approach to address the impact of climate change. In summary, the impacts of climate change on surface waters and groundwater in the Uluova Micro Basin include changes in water availability, water scarcity, and associated costs, and these have implications for agricultural water allocations and overall water management in the region. The study found that drier climate periods lead to reduced surface and groundwater input to farmland, resulting in increased water scarcity and scarcity costs. Conversely, periods characterized by wetter climates yield contrasting outcomes, alleviating water scarcity and its corresponding costs.

Groundwater inputs could be a significant but often overlooked source of phosphorus in lake ecosystems

Freshwater lakes are severely threatened, due largely to excess inputs of nutrients and other contaminants. Phosphorus (P) is receiving renewed attention due to recent increases in toxic cyanobacteria blooms in lakes worldwide. We investigated groundwater seepage for its role in P loading dynamics at Oneida Lake, New York, USA—one of the most well-studied lakes globally. P loading was measured at representative sites along the 88 km shoreline over three summers by directly measuring groundwater flow using seepage meters and porewater samplers. Groundwater seepage was a continuous and significant source of dissolved P over the summer months, comparable to tributary sources to the lake during that time. This constant input has enriched the concentrations of P in the nearshore surface waters, significantly above levels in the pelagic zone. Pore Total Phosphorus (TP) concentrations and loads reached extremely high values (up to 100 mg/L), with inorganic P representing only ~ 10% of TP per site. Groundwater seepage flows and P loadings were highly variable across space and time, partially explained by adjacent land uses and precipitation. Our research concludes that groundwater seepage is a significant, but overlooked, source of dissolved P and a crucial factor driving summer primary production at Oneida Lake, and likely other temperate lakes.

Unexpected contributions by carbonates and organic matter in a silicate-dominated tropical catchment: An isotope approach

The understanding of global carbon has rarely extended to small-scale tropical river basins. To address these uncertainties, this study aims to investigate the importance of rock weathering and organic matter turnover in the carbon cycle in a terrain dominated by crystalline silicate rocks. The geochemical composition of the dissolved and particulate carbon phases (DIC, DOC and POC) and their stable carbon isotopes were studied in the Deduru Oya River in Sri Lanka. Dissolved inorganic carbon (DIC) was the most dominant carbon phase and its contribution to the total carbon pool varied between 67 and 89 %. Furthermore, the δ13CDIC values in the river varied between −1.1 and −16.5 ‰. The lithological characteristics and molar ratios between Ca2+, Mg2+ and HCO3− indicated rock weathering mainly by CO2 and carbonic acid. The δ13CDIC values for groundwater input were −15.9 ‰, while for carbonate weathering, mainly due to fertiliser input, they reached a value of −12.7 ‰. This input was fed into an isotope mass balance to determine the relative contributions. However, the isotope mass balance was only plausible after correcting for the effects on δ13CDIC caused by degassing and photosynthesis. Our study demonstrated that carbonate weathering and organic matter turnover are essential components of the river carbon cycle even in a silicate dominated catchment. They can represent up to 60 % of the DIC pool. Combined with the higher organic matter turnover and high pCO2 in the river water, it can be suggested that the Deduru Oya River acts as a net source of CO2 in the atmosphere. Our study shows that CO2 degassing and in-stream photosynthesis in tropical river systems need to be considered along with chemical weathering to account for carbon transport and turnover in tropical rivers.

Diel temperature signals track seasonal shifts in localized groundwater contributions to headwater streamflow generation at network scale

Groundwater contributions to streamflow sustain aquatic ecosystem resilience; streams without significant groundwater inputs often have well-coupled air and water temperatures that degrade cold-water habitat during warm low flow periods. Widespread uncertainty in stream-groundwater connectivity across space and time has created disparate predictions of energy and nutrient fluxes across headwater networks, hindering predictions of cold-water habitat resilience under climate change scenarios. Recently, annual paired air and water temperature signals have been harnessed to indicate stream water thermal sensitivity and the dominance of deep versus shallow groundwater influence, although the utility of diel air–water temperature signal metrics for hydrologic inference has remained unexplored. Here we analyzed two consecutive years of locally paired, air–water temperature data from 47 headwater stream sites in the Catskill Mountains, New York, USA, and discovered characteristic seasonal patterns in diel temperature signal sinusoid metrics (amplitude ratio, phase lag, and mean ratio) driven by shifts in streamflow generation mechanisms and stream network position. Hydrologic interpretations of observed patterns were supported by stream heat budget model scenarios and additional analysis of paired air–water temperature data from two streams in Shenandoah National Park, Virginia, USA, with well characterized stream-groundwater connectivity. We found that within smaller tributaries, streamflow generation transitions from runoff to groundwater dominance were driven by hillslope drying during seasonal periods of lower precipitation. This was evidenced by significant correlations (p < 0.01) between daily water:air temperature signal amplitudes (non-linear decreases of ∼ 50 %) and derived baseflow index at 22 of the 28 sites, indicating enhanced local groundwater influence on streamflow promotes decoupling of diel air–water temperature signals. Additionally, ratios between daily water:air temperature signal means were lower in tributaries (∼0.68) when compared to main-stem (∼0.8) sites, increasing linearly throughout the observational period. In conceptual stream heat budget models, groundwater inflow had minimal effects on daily phase lags (∼0.2 hr), but increases in fractional groundwater discharge (0–50 %) depressed daily amplitude (∼20 % to 50 %) and mean ratios (∼15 %), supporting the sensitivity of daily metrics to interpreted changes in seasonal groundwater contributions to streamflow. During observational periods (i.e., April through October 2021 and 2022), significant differences (p < 0.01) between tributary and main-stem air–water metrics occurred when baseflow contributions were highest (∼0.93 vs. ∼ 0.68), as sites lower in the network had daily temperature metrics dominated by stream channel thermal inertia, rather than local groundwater connectivity, showing enhanced air–water diel signal coupling during warmer, drier periods. Divergent air temperature coupling across the network was interpreted as being driven by distance from local groundwater source zones, as additional lateral groundwater inflows do not contribute a meaningful fraction to channel discharge lower in the network. Given the growing footprint of stream temperature observations, diel air–water temperature signals can provide distributed metrics sensitive to upstream groundwater discharge. Consequently, these metrics can support ongoing efforts by resource managers and researchers seeking to forecast the resilience of cold-water habitat to climate warming and changing precipitation regimes in mountain headwater streams.

Indications of preferential groundwater seepage feeding northern peatland pools

Groundwater seepage from underlying permeable glacial sedimentary structures, such as eskers, has been hypothesized to directly feed pools in northern peat bogs. These hypotheses directly contradict classical peat bog models for ombrogenous systems, wherein meteoric water is the sole water input to these systems. Variations in the underlying mineral sediment in contact with the peat imply that unrecognized hydrogeologic connectivity may exist with pools in northern peat bogs, particularly where high permeability materials are in contact with the peat. Seepage dynamics originating from these structural variations were investigated using a suite of thermal and hydrogeophysical methods deployed around pools in a peat bog of northeastern Maine, USA. Thermal characterization methods mapped anomalies that were confirmed as matrix seepage or preferential flow pathways (PFPs). Geochemical methods were employed at identified thermal anomalies to confirm upwelling of solute-rich groundwater. Conduits around pools were associated with surficial terminations of suspected peat pipes, based on the inference of pathways extending down into the peat, that focus flow through PFPs in the peat matrix. Discharge also occurred through the peat matrix adjacent to suspected pipe structures and matrix seepage rates were quantified using analysis of diurnal temperature signals recorded at multiple depths. Seepage rates, with a maximum of nearly 0.4 m/d, were measured at localized points around pools. Periods of synchronized temperatures paired with highly muted diurnal temperature signals, recorded in diurnal temperature with depth data, were interpreted qualitatively as activation of strong upward discharge rates through suspected peat pipes. These time periods correlated strongly with local precipitation events around the peatland. Ground-penetrating radar surveys revealed discontinuities in the low permeability glacio-marine clay at the mineral sediment-peat interface, interpreted to be regional glacial esker deposits, which were located beneath and around pools. Heat tracing, specific conductance contrasts, seepage rates, and trace metal concentrations all imply groundwater seepage originating from underlying permeable glacial esker deposits and directly sourcing pools. Preferential groundwater inputs into northern peat bogs may play a key role in developing and maintaining pool systems, with enhanced solute transport impacting peatland ecology, water resources, and carbon cycling.

The response of ostracod faunal assemblages to hydrology, lake level, and carbon cycling in a Jamaican marl lake: a palaeolimnological investigation

Abstract. Ostracod taxa from shallow freshwater lakes are sensitive to a range of limnological factors including temperature, hydrological habitat, lake level, and the distribution of aquatic plants. Ostracod assemblages preserved in Quaternary lake sediments can be used to reconstruct limnological change and are therefore potentially valuable palaeoenvironmental proxies. However, lack of autecological information about some taxa may limit the validity of such reconstructions. We use fossil ostracod assemblages recovered from radiocarbon-dated late Holocene sediments from Wallywash Great Pond, a small, shallow freshwater lake in southwestern Jamaica, to reconstruct limnological change over the past ∼ 1800 years. We circumvent ongoing taxonomic and ecological uncertainties associated with the identification of fossil ostracod taxa by drawing on observations of the ecology of ostracods found living in Jamaican water bodies. By combining this information with limnological data from the extant lake, and with sedimentological and isotopic data from the lake sediments, we show that a published interpretation of ostracod assemblages for the late Quaternary of Wallywash Great Pond is simplistic, at least for the late Holocene section of the sediment record. We conclude that changes in ostracod assemblages are linked to variations in the input of undersaturated groundwater to the northern part of the lake from which the core was recovered. These variations, which were driven by changes in the precipitation / evaporation ratio (effective moisture), also controlled sedimentation, with reduced effective moisture and a decline in undersaturated groundwater input favouring marl precipitation, whereas organic sediments are linked to increased effective moisture and enhanced groundwater input. Our findings suggest that the dramatic shifts in ostracod assemblages at this site are a complex response to changes in hydrology, sedimentology, and carbonate saturation rather than being a simple indicator of lake-level change. Combining ostracod assemblage data with the results of other palaeolimnological analyses also allows more detailed reconstructions to be made for this lake, and such a multiproxy approach is recommended for similar lakes elsewhere.

Landscape influences on thermal sensitivity and predicted spatial variability among brook trout streams in the southeastern USA

AbstractWarming water temperatures as a result of climate change pose a major threat to coldwater organisms. However, the rate of warming is not spatially uniform due to surface‐ground‐water interactions and stream and watershed characteristics. Coldwater habitats that are most resistant to warming serve as thermal refugia and identifying their locations is critical to regional aquatic conservation planning. We quantified the thermal sensitivity of 203 streams providing current and potential habitat for brook trout (Salvelinus fontinalis) across nearly 1000 linear km of their native range in the southern and central Appalachian Mountains region, USA, and characterized their spatial variability with landscape variables available in the National Hydrography Dataset. Using the Bayesian framework, we calculated the maximum slope of the logistic function relating paired weekly mean air temperature and stream temperature as an index of stream thermal sensitivity. Streams differed greatly in thermal sensitivity and those with more resistant water temperature regimes (i.e., thermal refugia) were consistently characterized by southerly latitudes and groundwater input. Landscape variables derived from a principal component analysis explained 16% of the variation in thermal sensitivity, indicating that the existing landscape variables were modestly successful in explaining spatial thermal heterogeneity. Using our model and spatial interpolation, we predicted thermal sensitivity at 8695 stream segments potentially suitable for brook trout in the study region. Thermal refugia were more common southward presumably due to higher elevations, but elsewhere they were also clustered at finer spatial scales. Our analysis informs prioritizing habitat conservation and restoration of this native salmonid and other aquatic organisms that depend on coldwater habitats in a warming world.

Using Geochemical Tracers to Determine Seasonal Inputs of Freshwater to a Coastal Estuary: Biscayne Bay, FL

Biscayne Bay is a coastal estuary that historically relied on rainfall and groundwater inputs from the karst Biscayne aquifer. The construction of major canals along the coastline has released point-source freshwater inputs into the bay, detrimentally affecting the Bay’s ecosystem balance. This project investigates the proportional inputs of freshwater between the wet and dry seasons in Deering Estate, adjacent to Biscayne Bay. The objective of this project was accomplished by analyzing the water chemistry of the bay using naturally occurring geochemical tracers. Water sampling occurred from May to August (wet season 2022) and January to March (dry season 2023); at an inland freshwater spring and on Biscayne Bay. Water samples were analyzed for δ18O and δ2H values, and Sr2+/Ca2+ ratios as geochemical tracers. The highest and lowest salinity values observed in the wet and dry seasons, at both the freshwater spring and Biscayne Bay sites, were before and after a major rain event, respectively. The chemical analysis supports that rain is the dominant source of freshwater input into the bay at our sampling location, and the freshwater spring is dominated by groundwater and canal water during the wet season. During the dry season, groundwater and canal water are the dominant source for the sampling location in Biscayne Bay and the dominant source of freshwater input for the freshwater spring. However, all three endmembers contribute seasonally. Understanding freshwater inputs to this crucial estuary will provide important information for current restoration efforts of Biscayne Bay, specifically around the Deering Estate area.

Low Mo mobility during the laterization of ultramafic bedrock: Evidence from the East Sulawesi Ophiolite, Indonesia

Mo (isotope) cycling during the chemical weathering of ultramafic bedrock remains poorly quantified, mainly as a result of the analytical challenges caused by low Mo concentration and complex matrix effects in these rock types. Here, we utilize an improved chemical separation protocol that enables the extraction of Mo while reducing Ru and Fe matrix effects. We apply this method to lateritic weathering profiles developed over ultramafic bedrock in a high-intensity tropical weathering regime. The Mo concentrations in the laterite samples are higher (0.022 to 0.58 μg·g−1) than those of the peridotite bedrock (0.006 to 0.021 μg·g−1). The concentration-weighted average δ98Mo of the laterite profiles is −0.05‰ (n = 17), which is slightly higher but very close to the average δ98Mo of the peridotite bedrock (0.17 ± 0.21‰; 2SD; n = 5). Weakly-laterized samples show somewhat low δ98Mo with a minimum of −1.03‰ and Δ98Molaterite-bedrock up to −0.86‰, possibly as a result of preferential adsorption of liberated light Mo onto Fe (oxyhydr)oxides. In contrast, strongly-laterized samples show an overall Mo concentration gain and a slight isotopic shift towards higher bulk δ98Mo, with a maximum δ98Mo of +0.12‰ and Δ98Molaterite-bedrock up to +0.42‰. This likely reflects the re-scavenging of Mo released from weakly-laterized horizons to the ubiquitous Fe (oxyhydr)oxides, with potential superimposition of additional heavy Mo from atmospheric and/or groundwater input. Overall, this suggests a small contribution of dissolved Mo derived from ultramafic bedrock weathering in tropical settings to the aquatic environment.

Shifting groundwater fluxes in bedrock fractures: Evidence from stream water radon and water isotopes

Geologic features (e.g., fractures and alluvial fans) can play an important role in the locations and volumes of groundwater discharge and degree of groundwater-surface water (GW-SW) interactions. However, the role of these features in controlling GW-SW dynamics and streamflow generation processes are not well constrained. GW-SW interactions and streamflow generation processes are further complicated by variability in precipitation inputs from summer and fall monsoon rains, as well as declines in snowpack and changing melt dynamics driven by warming temperatures. Using high spatial and temporal resolution radon and water stable isotope sampling and a 1D groundwater flux model, we evaluated how groundwater contributions and GW-SW interactions varied along a stream reach impacted by fractures (fractured-zone) and downstream of the fractured hillslope (non-fractured zone) in Coal Creek, a Colorado River headwater stream affected by summer monsoons. During early summer, groundwater contributions from the fractured zone were high, but declined throughout the summer. Groundwater contributions from the non-fractured zone were constant throughout the summer and became proportionally more important later in the summer. We hypothesize that groundwater in the non-fractured zone is dominantly sourced from a high-storage alluvial fan at the base of a tributary that is connected to Coal Creek throughout the summer and provides consistent groundwater influx. Water isotope data revealed that Coal Creek responds quickly to incoming precipitation early in the summer, and summer precipitation becomes more important for streamflow generation later in the summer. We quantified the change in catchment dynamic storage and found it negatively related to stream water isotope values, and positively related to modeled groundwater discharge and the ratio of fractured zone to non-fractured zone groundwater. We interpret these relationships as declining hydrologic connectivity throughout the summer leading to late summer streamflow supported predominantly by shallow flow paths, with variable response to drying from geologic features based on their storage. As groundwater becomes more important for sustaining summer flows, quantifying local geologic controls on groundwater inputs and their response to variable moisture conditions may become critical for accurate predictions of streamflow.

Spring forth diversity: Specialist species contribute to the conservation value of headwater springs and streams at the landscape scale

AbstractHeadwater springs and streams often occur in relatively remote areas, reducing their exposure to human influences and thus increasing their collective capacity to support high biodiversity. Their aquatic macroinvertebrate communities can include species of conservation interest, some of which are specialists associated with groundwater inputs, low water temperature or temporary flow. However, the inaccessibility of some spring and stream networks has left their communities poorly characterized, limiting our capacity to implement effective conservation strategies. We characterized the biodiversity and conservation value of macroinvertebrate communities in a network of 51 relatively inaccessible and unimpacted headwater spring and stream sites spanning multiple catchments in a single landscape type: the chalk downland of south England. At each site, we kick sampled macroinvertebrate communities and recorded environmental variables, including flow permanence. To represent each community, we calculated taxa richness, coverage‐adjusted Hill‐Shannon diversity, the local contribution to beta diversity, and an index of richness and species rarity. We used the latter three metrics to rank sites based on their biodiversity and conservation value and analyzed relationships between metrics and environmental variables. We found specialists of springs, cold waters, groundwaters and temporary flow regimes, including rare species of conservation value. Some metrics responded to environmental variables, but top‐ranking sites had highly variable environmental characteristics. We highlight the value of individual headwater streams with contrasting characteristics as contributors to ecologically heterogeneous site networks. Our results can inform landscape‐scale management strategies that protect headwaters as refuges that support biodiverse communities, including rare species, as they adapt to global change.

Hydroclimatic Vulnerability of Wetlands to Upwind Land Use Changes

AbstractDespite their importance, wetland ecosystems protected by the Ramsar Convention are under pressure from climate change and human activities. These drivers are altering water availability in these wetlands, changing water levels or surface water extent, in some cases, beyond historical variability. Attribution of the effects of human and climate activities is usually focused on changes within the wetlands or their upstream surface and groundwater inputs. However, the reliance of wetland water availability on upwind atmospheric moisture supply is less understood. Here, we assess the vulnerability of 40 Ramsar wetlands to precipitation changes caused by land use and hydroclimatic change occurring in their upwind moisture‐supplying regions. We use moisture flows from a Lagrangian tracking model, atmospheric reanalysis data, and historical land use change (LUC) data to assess and quantify these changes. Our analyses show that historical LUC has decreased precipitation and terrestrial moisture recycling in most wetland hydrological basins, decreasing surface water availability (precipitation minus evaporation). The most substantial effects on wetland water availability occurred in the tropic subtropical regions of Central Europe and Asia. Overall, we found wetlands in Central Asia and South America to be the most vulnerable by a combination of LUC‐driven effects on runoff, high terrestrial precipitation recycling, and recent decreases in surface water availability. This study stresses the need to incorporate upwind effects of land use changes in the restoration, management, and conservation of the world's wetlands.

Assessment of the Impact of War on Concentrations of Pollutants and Heavy Metals and Their Seasonal Variations in Water and Sediments of the Tigris River in Mosul/Iraq

The war-related contamination of water and sediment of the Tigris River within the urban area of Mosul leads to seasonally independent exceedances of the WHO limit values for Cd, Pb, Cr, and Ni in water and sediments. Furthermore, exceedances consistently occur for conductivity, PO43−, and SO42−, as well as sporadically for salinity and COD in water samples, and consistently for salinity in sediment samples, highlighting the direct impact of war (ammunition, ignition of sulfur fields), as well as indirect effects (destroyed wastewater infrastructure). Conflict-related emissions from the former conflict zone (S5–S7) are highlighted by the sudden increases in load from S4 to S5, although partially masked by the discharge of highly polluted water from the Khosr River (between S3 and S4). Due to the sorption of sediments and the presumed wind-borne discharge of highly polluted particles into the Tigris River, sediments at S10 on the southern edge of Mosul showed the highest pollutant loads. Significant statistical differences were observed through T-test analyses for E.C., TDS, salinity, COD, PO43−, NO3−, SO42−, Cd, Pb, Zn, Cr, and Ni for water samples, as well as salinity, Cd, Pb, Zn, and Cr for the sediment samples for seasonal comparison. Since the percentage difference of water samples at S4–S7 is smaller than upstream and downstream, contaminant input is not limited to rainwater but also occurs via the year-round infiltration of highly polluted wastewater from the surrounding valleys or suburban areas, as well as presumably polluted groundwater or windblown particulate input.

Exploratory study of groundwater infiltration in lough arrow using thermal imagery and geochemical tracers

abstract: Groundwater dynamics were investigated in Lough Arrow in the north-west of Ireland. The lake is designated under the EU Habitats Directive (92/43/EEC) for its representative Annex I habitat from which charophytes are the main feature of interest. Groundwater interactions are considered a significant component of the lough's hydrology with its Annex I archetype deemed vulnerable to the pressures of nutrient pollution. This study utilised thermal imagery and geochemical tracers to detect and quantify groundwater inputs. Landsat 7 Thermal Infrared Imagery from two dates in both summer and winter was processed to investigate the potential occurrence of localised seepage points of groundwater captured as anomalous spatial plumes. In situ surveys of radon were undertaken in summer to confirm the presence of groundwater in the lake. Results were subsequently modelled to estimate the total groundwater discharge into the lake during the survey period. Additionally, a conceptual site model was created to characterise potential pressures to the lake from groundwater interactions within the catchment. Thermal imaging failed to conclusively identify thermal plumes consistent with localised groundwater inputs in Lough Arrow. However, the radon inventory applied to the mass balance estimated the lake was subject to 6,722m3 of groundwater influx per day at the time of the survey. The conceptual site model determined the lake was subject to potential pollution pressures from groundwater due to the catchment's physical attributes and land use activities. This is primarily due to the presence of a karst aquifer in the majority of the catchment coupled with significant agricultural and forestry practices. The vulnerability of the aquifer and the influx of groundwater to the lake highlights the potential threat groundwater contamination may pose to the favourable conservation condition of Lough Arrow's Annex I habitat.

Двадцать третья летняя научно-исследовательская экспедиция клуба Портулан в район г. Мунку-Сардык

Summarizes the results of the summer expeditions 2024 of the student-teaching club "Portulan" and the Institute of Geography named after V.B. Gubkin. V.B.Sochava SB RAS to the Munku-Sardyk mountain area, which included field research of nival and glacial formations, river ice, slope relief forms and hazardous processes in the valleys of the Bely Irkut and Muguvek rivers: weather and temperature regime were traditionally monitored over the entire vertical relief span, thermochron readings were taken, the stone stream "Active" was surveyed, summer condition of Peretolchina and Radde glaciers and snowfields was assessed, water samples were taken to assess the share of glacier, ground and surface water inputs.

Nitrogen and carbon cycling and relationships to radium behavior in porewater and surface water: Insight from a dry year sampling in a hypersaline estuary

Biogeochemical transformations within highly saline subterranean estuaries (STE) dramatically affect solute cycling, resulting in submarine groundwater discharge (SGD) with distinct chemical signatures. The study hypothesizes that biogeochemical processes within hypersaline bay porewaters (PW) simultaneously affect nitrogen, carbon, and radium cycling. We measured radium isotopes (226Ra, 224Ra, and 223Ra), nutrients (dissolved inorganic nitrogen [DIN: NH4+ + NO2− + NO3−], HPO42− [DIP], HSiO3− [DSi], dissolved organic carbon [DOC]), total alkalinity (TA), dissolved inorganic carbon (DIC), stable isotopes, and major cations in PW and surface water (SW) of Baffin Bay, a well-mixed, semi-enclosed estuary along the semiarid northwestern Gulf of Mexico coast, over three seasons in a characteristically dry year. This study's findings show a concurrent increase in NH4+, DIP, DSi, and TA/DIC with reduced metal species (e.g., Mn and Fe) and Ra during the hot and dry seasons, particularly in PW, under increasingly reducing conditions. Principal component analyses (PCA) suggest these increases are primarily driven by dissimilatory nitrate/nitrite reduction to ammonium (DNRA) and dissolution of lithogenic particles and biogenic CaCO3, modulated by organic matter degradation or remineralization. While more significant terrestrial groundwater inputs may contribute to solutes and Ra supply in the STE, the biogeochemically induced variability in solute concentrations in PW primarily drives larger SGD-derived fluxes, particularly notable in hot months. During a typically dry year, these fluxes, estimated as the average of 226Ra and 223Ra mass balance models (e.g., July/November fluxes in Mmol∙d−1: 0.093/0.092 of NO3−; 0.2/0.02 of NO2−; 72/16 of NH4+; 72.2/18 of DIN; 1.5/0.2 of HPO42−; 20/9 of HSiO3−; 42/37 of DOC; 503/399 of TA; 582/431 of DIC) are orders of magnitude (∼4 for DIN and DIC, ∼3 for DIP, DSi, and DOC, and ∼2 for TA) greater than surface runoff inputs. These substantial SGD inputs likely sustain phytoplankton growth and potentially fuel harmful algal blooms while countering estuarine acidification.

Nutrient inputs shape ecosystem functioning gradients along the pristine, upper Neretva River, Bosnia and Herzegovina

Ecosystem functions are the backbone of ecosystem services that rivers provide to human societies. Ecosystem functioning emerges from the interaction between biological communities and their environment. As environmental conditions in rivers change along their longitudinal continuum, so does functioning. Sometimes, these changes do not follow smooth gradients but rather great discontinuities. This can be the case in calcareous, karstic rivers due to the sudden massive inputs of groundwater along the landscape, a typical phenomenon for Balkan rivers. Despite their high geodiversity and their great ecological value, Balkan rivers remain understudied. Here, we investigated how ecosystem functions and their diversity (estimated as multifunctionality) change along the continuum of the karstic, free-flowing Neretva River in Bosnia and Herzegovina. For this purpose, we measured a subset of fundamental ecosystem functions (ecosystem gross primary production, biofilm net primary production and enzymatic activities, organic matter decomposition) in 11 river reaches from the Neretva headwaters to river sections upstream of the Jablanica reservoir. We found different functions reached their maximum in different sections of the Neretva depending on nutrient inputs. While organic matter decomposition was highest in headwaters due to the input of nutrients from riparian vegetation, biofilm enzymatic activity expressed highest values at middle sections due to groundwater inputs of NH4+-N. Primary production was highest at the most downstream sections due to the accumulation of NO3--N and PO43--P within the catchment area. As a result, average multifunctionality peaked at sites with the highest nutrient concentration across the Neretva river continuum, indicating a stronger influence of nutrient inputs than network position. The pristine conditions of the Neretva result in oligotrophic conditions along its upper course. Our results emphasize the great sensitivity of ecosystem functioning in the Neretva to nutrient inputs and environmental discontinuities, either natural or human-made. Potential major, long-term impacts in the area might alter existing environmental gradients and thus ecosystem functioning in rivers at local and regional scale.

Microgeographic variation in demography and thermal regimes stabilize regional abundance of a widespread freshwater fish.

Predicting the persistence of species under climate change is an increasingly important objective in ecological research and management. However, biotic and abiotic heterogeneity can drive asynchrony in population responses at small spatial scales, complicating species-level assessments. For widely distributed species consisting of many fragmented populations, such as brook trout (Salvelinus fontinalis), understanding the drivers of asynchrony in population dynamics can improve the predictions of range-wide climate impacts. We analyzed the demographic time series from mark-recapture surveys of 11 natural brook trout populations in eastern Canada over 13 years to examine the extent, drivers, and consequences of fine-scale population variation. The focal populations were genetically differentiated, occupied a small area (~25 km2 ) with few human impacts, and experienced similar climate conditions. Recruitment was highly asynchronous, weakly related to climate variables and showed population-specific relationships with other demographic processes, generating diverse population dynamics. In contrast, individual growth was mostly synchronized among populations and driven by a shared positive relationship with stream temperature. Outputs from population-specific models were unrelated to four of the five hypothesized drivers (recruitment, growth, reproductive success, phylogenetic distance), but variation in groundwater inputs strongly influenced stream temperature regimes and stock-recruitment relationships. Finally, population asynchrony generated a portfolio effect that stabilized regional species abundance. Our results demonstrated that population demographics and habitat diversity at microgeographic scales can play a significant role in moderating species responses to climate change. Moreover, we suggest that the absence of human activities within study streams preserved natural habitat variation and contributed to asynchrony in brook trout abundance, while the small study area eased monitoring and increased the likelihood of detecting asynchrony. Therefore, anthropogenic habitat degradation, landscape context, and spatial scale must be considered when developing management strategies to monitor and maintain populations that are diverse, stable, and resilient to climate change.