Catchment Land Use Research Articles

Assessment of pollution and other impairments of US reservoirs based on expert opinion

A comprehensive understanding of the prevailing pollution and other impairments to reservoirs is necessary at the national level to analyze patterns and causes as well as allocate national resources effectively. Most of these impairments are associated with sedimentation, nutrient contamination, and other pollution factors. The costs involved in conducting on-site surveys at multiple locations are potential obstacles for obtaining empirical data on large-scale spatial impairments. In such cases, inputs from specialists may be required to offset the absence of empirical data for determining the impairment statuses of thousands of geographically dispersed reservoirs. Thus, our aim was to examine whether expert opinion could offer a comprehensive review of the impairment statuses of numerous reservoirs in the United States. We designed and executed an internet-based survey of reservoir specialists to gather their ratings on visually evident elements of reservoir impairment. To evaluate the ratings, we searched for correlations with factors known to have impacts on reservoir impairment. Canonical correlation analyses indicated that nine metrics used by experts to rate impairment levels on an ordinal scale were correlated with metrics descriptive of the physical qualities of reservoirs, land use in catchments, and prevailing local climate. We thus conclude that expert opinions may facilitate assessments of impairment levels over large geographical areas. Lastly, we define the circumstances under which it is permissible to rely on expert opinions and propose criteria that could improve the quality of the data collected.

Effects of mixed land use on urban stormwater quality under different rainfall event types

The joint effect of mixed land uses and rainfall event types was studied using a two-year field monitoring program in four urban catchments in Calgary, Alberta, Canada. Event mean concentration (EMC) and event pollutant load (EPL) were employed to evaluate the total suspended sediment (TSS), nitrogen and phosphorus. The correlation analysis showed that most nitrogen and phosphorus components (except for NO2−/NO3− and TDP) predominantly exist in particulate form in the study areas. The correlation for EPL was notably stronger than EMC, which can be attributed to varying rainfall characteristics. The differences in EMCs and EPLs of TSS, nitrogen and phosphorus across catchments indicated that the complexity and spatial distribution of mixed land use can influence the generation and transportation of pollutants in urban runoff. The impacts of rainfall characteristics on stormwater quality are integrated rather than driven by a single rainfall characteristic. Brief but intense events tended to elevate TSS, nitrogen and phosphorus concentrations, especially in complex land-use catchments. Events with long antecedent dry days and short duration also resulted in increased pollutant concentrations, while events with long duration and low intensity could result in higher EPLs. The effect of mixed land use on water quality can vary depending on rainfall event types. Seasonal variations were found in EMC and EPL of TSS, nitrogen and phosphorus, with higher values in the spring and summer than the fall. Seasonal variations are mainly influenced by rainfall conditions, temperature and anthropogenic activities (e.g. lawn fertilization and de-icing with sands). MLR considering rainfall characteristics is an effective method for predicting stormwater quality within a single catchment. Considering complexity and spatial distribution of mixed land use can improve the accuracy of the harmonized MLR model. This research provided insights into understanding the complexities introduced by mixed land use and rainfall event types in urban stormwater quality.

Plutonium isotopes can be used to model soil erosion in Kenya

Climate change poses an immediate threat to tropical soils with changes in rainfall patterns resulting in accelerated land degradation processes. To ensure the future sustainability of arable land, it is essential to improve our understanding of the factors that influence soil erosion processes. This work aimed to evaluate patterns of soil erosion using the activity of plutonium isotopes (Pu) at sites with different land use and clearance scale in the Winam Gulf catchment of Lake Victoria in Kenya. Erosion rates were modelled at potential erosive sites using the MODERN model to understand small-scale erosion processes and the effect of different management practices. The lowest soil redistribution rates for arable land were 0.10 Mg ha−1 yr−1 showing overall deposition, resulting from community-led bottom-up mitigation practices. In contrast erosion rates of 8.93 Mg ha−1 yr−1 were found in areas where steep terraces have been formed. This demonstrates the significance of community-led participation in effectively managing land degradation processes. Another key factor identified in the acceleration of soil erosion rates was the clearance of land with an increased rate of erosion over three years reported (0.45 to 0.82 Mg ha−1 yr−1) underlining the importance vegetation cover plays in limiting soil erosion processes. This novel application of fallout plutonium as a tracer, highlights its potential to inform the understanding of how soil erosion processes respond to land management, which will better support implementation of effective mitigation strategies.Graphical abstractModelling of soil erosion and deposition patterns using the MODERN model to calculate the depth of soil loss/gain.

Exploring freshwater stream bacterial communities as indicators of land use intensity

BackgroundStream ecosystems comprise complex interactions among biological communities and their physicochemical surroundings, contributing to their overall ecological health. Despite this, many monitoring programs ignore changes in the bacterial communities that are the base of food webs in streams, often focusing on stream physicochemical assessments or macroinvertebrate community diversity instead. We used 16S rRNA gene sequencing to assess bacterial community compositions within 600 New Zealand stream biofilm samples from 204 sites within a 6-week period (February–March 2010). Sites were either dominated by indigenous forests, exotic plantation forests, horticulture, or pastoral grasslands in the upstream catchment. We sought to predict each site’s catchment land use and environmental conditions based on the composition of the stream bacterial communities.ResultsRandom forest modelling allowed us to use bacterial community composition to predict upstream catchment land use with 65% accuracy; urban sites were correctly assigned 90% of the time. Despite the variation inherent when sampling across a ~ 1000-km distance, bacterial community data could correctly differentiate undisturbed sites, grouped by their dominant environmental properties, with 75% accuracy. The positive correlations between actual values and those predicted by the models built using the stream biofilm bacterial data ranged from weak (average log N concentration in the stream water, R2 = 0.02) to strong (annual mean air temperature, R2 = 0.69).ConclusionsFreshwater bacterial community data provide useful insights into land use impacts on stream ecosystems; they may be used as an additional measure to screen stream catchment attributes.

Assessing the combined effects of catchment land use and runoff on estuarine fish assemblages

Connectivity between land and sea through the movement of species, energy and nutrients means that land-based impacts can affect the structure and functioning of nearby coastal ecosystems. As the interface between land and sea, estuaries are often faced with increasing pressures from catchment modifications (e.g. the removal of terrestrial vegetation) which can alter the overall health of estuaries (e.g. the degradation of coastal water quality due to an increase in terrestrial runoff) and change the value of habitat for many marine species. These landscape-scale impacts can, however, be mediated through variations in the context and connectivity of seascapes (e.g. greater extent of vegetated ecosystems help to filter nutrients). We surveyed fish across five estuaries over four years using underwater videography and sought correlations between fish biodiversity and abundance with variables indexing catchment land use, seascape connectivity, and coastal water quality. Fish assemblages were more abundant and diverse at sites which had lower chlorophyll-a concentrations and were nearer to the estuary mouth, in conjunction with catchments containing higher percent of natural land and heterogenous seascapes. Sites with lower concentrations of chlorophyll-a supported indicator species from more diverse functional groups that had greater fisheries values, in comparison to indicator species from sites with high concentrations of chlorophyll-a. This research can help direct coastal management to better prioritise management in coastal ecosystems, thereby enhancing fish richness and abundance, functional group richness and fisheries value.

Examining chlorophyll-a concentrations in tropical reservoirs under various land use changes using Sentinel – 2 and Google Earth engine – Bhadra and Tungabhadra, India

The understanding of spatio-temporal variation in land use and land cover (LULC) patterns is crucial for managing catchment land use planning, as it directly influences of tropical reservoir water quality and the subsequent Nutrient Contamination (NC) of unmonitored water bodies. The current research attempts to accurately measure the influence of LULC and its associated determinants on the quantities of NC loads by using Chl-a as a proxy, within tropical reservoirs, i.e. Bhadra and Tungabhadra, located in same river catchment. This Chl-a spread calculated by the Maximum Chlorophyll Index (MCI) derived from Sentinel 2 satellite data products covering the period from July 2016 to June 2021 were done using Google Earth Engine (GEE) platform. The validation analysis confirms the robustness of the methodology with a strong correlation between MCI-calculated values and EOMAP (Earth Observation and Environmental Services Mapping) Chl-a (μg/L) data points for both reservoirs, Bhadra (R2 = 0.64) and Tungabhadra (R2 = 0.68). The findings reveal that, Tungabhadra reservoir consistently exhibits an excessive spatial distribution of Chl-a spread area (17 km2 to 335 km2), reflecting nutrient-rich water inflows, particularly evident during the post-monsoon period. This notable rise could be linked to harvesting the Kharif crop, resulting in elevated nutrient concentrations. In contrast Bhadra reservoir, dominated by forested areas, maintains relatively lower Chl-a spread areas (<20 km2), highlighting its pivotal role in maintaining water cleanliness and serves as a riparian boundary. In addition, the changes in LULC classes show a strong relationship with variation in Chl-a during the studied period, for the Bhadra Reservoir R2 = 0.51 (F- statistics = 3.983, p = 0.021), and the Tungabhadra Reservoir R2 = 0.802 (F- statistics = 7.489, p = 0.0143). This highlights how changes in land use significantly shape contamination dynamics, deepening our understanding of nutrient inputs and contamination drivers in tropical reservoirs.

Quantitative fecal source characterization of urban municipal storm sewer system outfall ‘wet’ and ‘dry’ weather discharges

Urban areas are built environments containing substantial amounts of impervious surfaces (e.g., streets, sidewalks, roof tops). These areas often include elaborately engineered drainage networks designed to collect, transport, and discharge untreated stormwater into local surface waters. When left uncontrolled, these discharges may contain unsafe levels of fecal waste from sources such as sanitary sewage and wildlife even under dry weather conditions. This study evaluates paired measurements of host-associated genetic markers (log10 copies per reaction) indicative of human (HF183/BacR287 and HumM2), ruminant (Rum2Bac), canine (DG3), and avian (GFD) fecal sources, 12-hour cumulative precipitation (mm), four catchment land use metrics determined by global information system (GIS) mapping, and Escherichia coli (MPN/100 ml) from seven municipal separate storm sewer system outfall locations situated at the southern portion of the Anacostia River Watershed (District of Columbia, U.S.A.). A total of 231 discharge samples were collected twice per month (n = 24 sampling days) and after rain events (n = 9) over a 13-month period. Approximately 50 % of samples (n = 116) were impaired, exceeding the local E. coli single sample maximum of 2.613 log10 MPN/100 ml. Genetic quality controls indicated the absence of amplification inhibition in 97.8 % of samples, however 14.7 % (n = 34) samples showed bias in DNA recovery. Of eligible samples, quantifiable levels were observed for avian (84.1 %), human (57.4 % for HF183/BacR287 and 40 % for HumM2), canine (46.7 %), and ruminant (15.9 %) host-associated genetic markers. Potential links between paired measurements are explored with a recently developed Bayesian qPCR censored data analysis approach. Findings indicate that human, pet, and urban wildlife all contribute to storm outfall discharge water quality in the District of Columbia, but pollutant source contributions vary based on ‘wet’ and ‘dry’ conditions and catchment land use, demonstrating that genetic-based fecal source identification methods combined with GIS land use mapping can complement routine E. coli monitoring to improve stormwater management in urban areas.

Effects of catchment land use on temperate mangrove forests

Human land use changes are threatening the integrity and health of coastal ecosystems worldwide. Intensified land use for anthropogenic purposes increases sedimentation rates, pollutants, and nutrient concentrations into adjacent coastal areas, often with detrimental effects on marine life and ecosystem functioning. However, how these factors interact to influence ecosystem health in mangrove forests is poorly understood. This study investigates the effects of catchment human land use on mangrove forest architecture and sedimentary attributes at a landscape-scale. Thirty sites were selected along a gradient of human land use within a narrow latitudinal range, to minimise the effects of varying climatic conditions. Land use was quantified using spatial analysis tools with existing land use databases (LCDB5). Twenty-six forest architectural and sedimentary variables were collected from each site. The results revealed a significant effect of human land use on ten out of 26 environmental variables.Eutrophication, characterised by changes in redox potential, pH, and sediment nutrient concentrations, was strongly associated with increasing human land use. The δ15N values of sediments and leaves also indicated increased anthropogenic nitrogen input. Furthermore, the study identified a positive correlation between human land use and tree density, indicating that increased nutrient delivery from catchments contributes to enhanced mangrove growth. Propagule and seedling densities were also positively correlated with human land use, suggesting potential recruitment success mechanisms. This research underpins the complex interactions between human land use and mangrove ecosystems, revealing changes in carbon dynamics, potential alterations in ecosystem services, and a need for holistic management approaches that consider the interconnectedness of species and their environment. These findings provide essential insights for regional ecosystem models, coastal management, and restoration strategies to address the impacts of human pressures on temperate mangrove forests, even in estuaries that may be relatively healthy.

Nitrogen Assimilation and Nitrification in Surface Waters of the Amazon and Pará Estuaries

AbstractUnder increasing anthropogenic impacts, the hydrology, weathering, turbidity, and biogeochemistry of the Amazon and Pará river catchments are changing, potentially affecting the concentration and speciation of nitrogen (N) entering the estuary, as well as the subsequent primary productivity. Primary production and several N‐cycling rates have been studied in the northern river plume, and new studies focusing on specific processes in the river mouth emerged. Yet, a general overview is still lacking. For the first time, we provide an overview of primary production along with nitrification, ammonium (NH4+), nitrate (NO3−), and amino acid uptake rates in the Amazon and Pará river mouths which exhibit different degrees of catchment land use. Our results indicate that the Amazon supplies tenfold more NH4+ and NO3−, and its nitrification rates are four times higher than in the Pará River. The stable isotope composition of ambient water and NO3− confirmed that nitrification is a dominant pathway, with fluxes reaching 8.5 × 108 mol N d−1 in the Amazon. Nutrients are transported to regions with reduced turbidity and little nitrification, facilitating NH4+ (0.2–2.4 × 108 mol N d−1) and carbon uptake (4.6 and 14.0 × 108 mol C d−1 in the Pará and the Amazon, respectively) by phytoplankton. The lower N‐cycling rates measured in the Pará relative to the Amazon River mouth likely originate from differences in river discharge and watershed characteristics.

Determination of Heavy Metal Sources in an Agricultural Catchment (Poland) Using the Fingerprinting Method

This study investigates the heavy metal contamination of soils and suspended sediments in the Nurzec River catchment (Eastern Poland), focusing in particular on the effects of catchment land use. The fingerprinting technique has been combined with the classic, Igeo, and EF index-supported contamination analysis to identify heavy metals sources. A wide range of elements (31 chemical elements including heavy metals) allowed the author to analyse the pathways and to identify the pressures of heavy metal contamination. The developed statistical models of heavy metal source distribution displayed results at a statistically significant level. The results have revealed the significant impact of land use connected with urban areas (URBAN) and pastures (PAST), which together constitute less than 20% of the river catchment area. These results are relevant to the local authorities and stakeholders, as they highlight the significant impact of low-density urban areas that are not locally considered as the major sources of heavy metal pollution. These results will contribute to sustainable decisions in the field of contaminated catchment area remediation.

Modeling streamflow responses to land use and land cover change using MIKE SHE model in the upper Omo Gibe catchment of Ethiopia

AbstractThe land use and land cover (LULC) changes in the upper Gibe catchment were studied intricately using the MIKE SHE model and analyzed through statistical tests. The Mann–Kendall test was used to identify potential trends, while the Pettit test was used to detect abrupt changes in rainfall, temperature, and streamflow. A set of three maps of LULC change (1990, 2003, and 2018) was developed to observe how they affect the hydrological pattern of the catchment. Statistical analyses were conducted at mean annual time scales to establish relationships among the anomalies. It has been noted that certain temperature gauges showed statistically significant increases in temperature. Change points in the 1980s and 1990s were identified during the study period. The annual streamflow trends displayed an increasing trend that was not that significant. LULC changes contributed to increased surface runoff, attributed to agricultural, settlement, and water body expansion, as well as reductions in bare land, forest, shrubland, and grassland. The MIKE SHE model performed well during both the calibration and validation periods on the monthly time scale. The alterations in LULC had a noticeable impact on stream flows during both wet and dry seasons, resulting in increased mean monthly stream flows during the wet season and decreased flows during the dry season. The MIKE SHE study and related statistical analysis is quite a different method to perceive the results.

Relationship between land use and water quality in a tropical urban catchment of the Congo Basin: A case study of N'Djili River catchment

Abstract This study focuses on N'Djili River catchment, a vital water source in Kinshasa that undergoes anthropogenic pressure and land use changes. The lower course of the river is particularly affected by uncontrolled urbanization, informal settlements, improper waste management practices, and vegetation degradation. The aim of this study is to determine the relationship between land use and river water quality in this catchment. Water samples were collected for physico-chemical and bacteriological analysis from 10 sampling sites along the river course. Land use categories were determined using Sentinel-2 land cover imageries and buffer scaling techniques. A redundancy analysis (RDA) was conducted to determine the relationship between land use categories and water quality variables. The laboratory analysis revealed physical, chemical, and biological pollution of the river waters. The RDA results showed that 70% of water quality parameters were explained by the studied land use categories. The urbanized area was the most significant explanatory variable at all buffer scales, negatively impacting water quality parameters. Conversely, trees and range lands had a positive impact on water quality. The study concludes that further research is needed to assess the extent of water pollution and develop integrated management strategies for minimizing pollution in this catchment.

Surface Water (SW) and Shallow Groundwater (SGW) Nutrient Concentrations in Riparian Wetlands of a Mixed Land-Use Catchment

Precipitation patterns, water flow direction, and local land-use practices affect surface water (SW) and shallow groundwater (SGW) nutrient concentrations in riparian wetlands. Given physical process complexities, spatiotemporal quantification of nutrients and physical factors influencing nutrient concentrations are needed to advance wetland water resource management. To address these needs, a study was conducted in riparian wetlands of a mixed land-use catchment in West Virginia (WV), USA. Observed data included SW–SGW levels and nutrient concentrations, including nitrate (NO3-N), nitrite (NO2-N), ammonium (NH4-N), orthophosphate (PO43-P), total nitrogen (total_N), and total phosphorus (total_P) from January 2020 to December 2021. Water samples were collected monthly from stream gauge sites (n = 4) and co-located piezometers (n = 13). Results showed that, on average, gaining stream conditions were observed in upstream sites, and losing stream conditions were observed in downstream sites. Observed nutrient profiles between SW and SGW included SW exhibiting a higher average NO3-N concentration (0.42 mg/L), while SGW displayed an elevated NH4-N concentration (1.55 mg/L) relative to other nitrogen species. Significantly high (p &lt; 0.05) SW NO3- concentrations in summer and fall were attributed to increased precipitation and corresponding water level and, therefore, pressure head and transport fluctuations. Principal Component Analysis (PCA) showed differences in nutrient concentrations based on the water source type and catchment land use, explaining 65% of data variability. Spearman correlation analysis illustrated the correlation among nutrient concentrations, land use, and water level changes in SW and SGW environments. This study provides needed baseline data on nutrient dynamics for a riparian wetland in a mixed land-use catchment, supplying science-based information to advance land and water management practices in the study watershed and similar physiographic watersheds globally.

Hindcasting estuary ecological states using sediment cores, modelled historic nutrient loads, and a Bayesian network

Estuaries are impacted by catchment land use changes, driving degradation associated with eutrophication and alterations in sediment dynamics. Estuarine ecological monitoring has typically covered only recent periods, so magnitudes and trajectories of degradation are often poorly described. Here, we develop a multi-method approach to hindcast historic estuary condition. We determined geochemical properties in dated sediment cores from two sites in the eutrophic New River Estuary (NRE), Aotearoa New Zealand. Mud, organic matter, carbon, and nitrogen (N) contents increased from ~1847 to 2019 (~20 to 100%, ~1 to ~7%, ~0.2 to ~3%, and ~0.03 to ~0.37% respectively). Historic land use modelling shows increasing catchment loads and water column total N rising from 165 to 663 mg m-3, with more rapid change in the late 20th and early 21st centuries. Strong correlations (R2 = 0.93-0.95) were found between sediment N content and water column N concentrations. Trophic indicators hindcasted by a Bayesian Belief Network worsened from the mid-20th to 21st centuries. This degradation is associated with increased sheep, beef and dairy farming in the catchment. Our approach identifies nutrient and sediment loadings associated with ‘tipping points’ for indicators and can inform policy by identification of hazardous levels of contaminant loading for other estuaries.

The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management

AbstractElevated fine sediment accumulation in a river system's gravel bed is known to cause detrimental ecological impacts. Current sediment targets and approaches to mitigation have failed due to the oversimplification of geomorphological processes controlling fine sediment accumulation and the lack of relevant scientific knowledge underpinning them. This is particularly apparent in chalk streams (groundwater‐dominated systems) which regularly exhibit high rates of sediment accumulation despite low suspended sediment yields. A necessary first step is to better characterise their sedimentology; thus, the novelty of this study was to determine the sedimentological characteristics of chalk stream gravel beds, specifically the quantity and distribution of fine sediment with depth. We collated published and unpublished freeze‐core data, encompassing 90 sites across 11 UK chalk streams. Results showed average quantities of fine sediment (&lt;2 mm) in chalk stream gravel beds were 25% by weight, with &gt;75% of beds exceeding thresholds for ecological degradation. Quantities of fine sediment increased with increasing depth into the bed, with an average increase between surface and subsurface layers of 54%, and 89% of the gravel bed over‐saturated with fine sediment. Regional differences were attributed to differences in stream power and local sediment sources, including surficial geology and catchment land use. Additionally, a major contrast was identified between experimental conditions in flume studies used to establish models describing interactions/mechanisms of fine sediment infiltration into immobile gravel beds and the natural conditions observed in chalk streams. As such, the use of such models as a basis to explore sediment management scenarios is unlikely to predict the outcome of such management techniques correctly in a real‐world situation.

Land use in catchments of small streams and a hydrological urban heat island – a case study in Kielce city (Poland)

ABSTRACT This article presents the spatial and temporal value and dynamics of water temperature in small streams flowing through a city of 200,000 inhabitants. The analysis is based on stationary measurements of a water temperature in eight (8) catchment outlets of various uses (including forest, suburban, urbanised). The water temperature was measured daily for 4 years (06 UTC; electronic thermometers; accuracy: 0.1°C). The study has shown that the water temperature in streams is clearly modi fied by the nature of land use prevailing in the catchment, represented by the imperviousness index. Urbanised areas caused a significant increase in minimum, mean and maximum temperature values on a daily, monthly and annual cycle. The determined relationship indicates that every 1% increase in impervious catchment area causes a water temperature increase of 0.1°C. The presented and documented facts justify the use of the term ‘hydrological urban heat island’, which began to appear in the literature.

Water Framework Directive micropollutant monitoring mirrors catchment land use: Importance of agricultural and urban sources revealed

River monitoring programs worldwide consistently unveil micropollutant concentrations (pesticide, pharmaceuticals, and industrial chemicals) exceeding regulatory quality targets with deteriorating effects on aquatic communities. However, both the composition and individual concentrations of micropollutants are likely to vary with the catchment land use, in particular regarding urban and agricultural area as the primary sources of micropollutants. In this study, we used a dataset of 109 governmental monitoring sites with micropollutants monitored across the Federal State of North Rhine-Westphalia, Germany, to investigate the relationship between high-resolution catchment land use (distinguishing urban, forested and grassland area as well as 22 different agricultural crop types) and 39 micropollutants using Linear Mixed Models (LMMs). Ecotoxicological risks were indicated for mixtures of pharmaceutical and industrial chemicals for 100 % and for pesticides for 55 % of the sites. The proportion of urban area in the catchment was positively related with concentrations of most pharmaceuticals and industrial chemicals (R2 up to 0.54), whereas the proportions of grassland and forested areas generally showed negative relations. Cropland overall showed weak positive relationships with micropollutant concentrations (R2 up to 0.29). Individual crop types, particularly vegetables and permanent crops, showed higher relations (R2 up to 0.46). The findings suggest that crop type-specific pesticide applications are mirrored in the detected micropollutant concentrations. This highlights the need for high-resolution spatial land use to investigate the magnitude and dynamics of micropollutant exposure and relevant pollution sources, which would remain undetected with highly aggregated land use classifications. Moreover, the findings imply the need for tailored management measures to reduce micropollutant concentrations from different sources and their related ecological effects. Urban point sources, could be managed by advanced wastewater treatment. The reduction of diffuse pollution from agricultural land uses requires additional measures, to prevent pesticides from entering the environment and exceeding regulatory quality targets.

Temporal change in urban fish biodiversity-Gains, losses, and drivers of change.

Our aim was to examine temporal change in alpha and beta diversity of freshwater fish communities in rivers that have urbanized over the same period to understand the influence of changes in land use and river connectivity on community change. We used biological (2001-2018), land use (2000-2015), and connectivity data (1987-2017) from Toronto, Ontario, Canada. We used linear mixed effects models to determine the strength of upstream land use, connectivity, and their changes over time to explain temporal change in alpha and beta diversity indices. We examined beta diversity using the temporal beta diversity index (TBI) to assess site-specific community change.The TBI was partitioned into gains and losses, and species-specific changes in abundance were assessed using paired t-tests. There were more gains than losses across the study sites as measured by TBI. We found little to no significant differences in species-specific abundances at aggregated spatial scales (study region, watershed, stream order). We found different relationships between landscape and connectivity variables with the biodiversity indices tested; however, almost all estimated confidence intervals overlapped with zero and had low goodness-of-fit. More fish biodiversity gains than losses were found across the study region, as measured by TBI. We found TBI to be a useful indicator of change as it identifies key sites to further investigate. We found two high value TBI sites gained non-native species, and one site shifted from a cool-water to warm-water species dominated community, both of which have management implications. Upstream catchment land use and connectivity had poor explanatory power for change in the measured biodiversity indices. Ultimately, such spatial-temporal datasets are invaluable and can reveal trends in biodiversity useful for environmental management when considering competing interests involved with urban sprawl in the ongoing "Decade on Restoration."

Combining isotopic and elemental tracers for enhanced sediment source partitioning in complex catchments

Sediment fingerprinting quantifies soil erosion processes by tracing sediment origins in water bodies. In this regard, several types of tracers have been used to discriminate different sediment sources. Stable isotopic composition of fatty acids is associated with land use/vegetation cover, while elemental composition is related to different mineralogy. Isotopic tracers are characterised by their isotopic ratio and total content, requiring specific fingerprinting models. Consequently, this has led to few studies combining elemental and isotopic tracers.In this context, our analysis explores merging isotopic and elemental tracers to identify sediment sources in an ungauged Mediterranean mountain catchment. This catchment features consistent lithology, seasonal streams, and a history of land use changes, shifting from rangelands to croplands for increased agricultural production and later reverting to natural revegetation due to mid-20th-century land abandonment. Achieving effective source discrimination in these intricate landscapes remains a significant challenge, emphasising the need for diverse tracer integration.To explore this possibility, we collected composite source samples from three distinct land uses: cropland, Mediterranean forest, and pine forest, as well as two geomorphic features: highly disturbed areas such as exposed subsoil and channel banks. By considering these diverse sampling locations, we aim to capture the variability in sediment sources within the catchment. Our dataset spans one full hydrological year, allowing us to analyse sediment dynamics throughout different seasons and hydrological events.First, the Conservative Balance (CB) method was applied to integrate isotopic ratio and total content of each fatty acid into a single weighted tracer. Combining the weighted fatty acid (WFA) with elemental composition tracers significantly enhanced source discrimination, underlining the utility of employing diverse tracers for challenging source discrimination.The apportionment results revealed that agriculture, channel banks, and subsoils were the primary contributors, accounting for an average contribution of 29%, 39%, and 30% across most seasons. In contrast, sediment sources characterised by more permanent vegetation cover and minimal human influence, such as pine afforestation and Mediterranean forest, exhibited negligible contributions. The findings indicate the substantial impact of agricultural practices in Mediterranean agroecosystems, especially during storm events, on catchment hydrodynamics and sediment export. Additionally, despite their limited coverage, degraded areas significantly contributed to overall sediment dynamics through severe soil loss.By unravelling the hydrological implications of these sediment sources, our study provides valuable insights into the interplay between land use, hydrological processes, and sediment dynamics in Mediterranean mountain catchments.

Catchment land use effect on mercury concentrations in lake sediments: A high-resolution study of Qinghai Lake

Mercury (Hg) contamination in aquatic environments presents a significant ecological and human health concern. This study explored the relationship between catchment land use and Hg concentrations within Qinghai Lake sediment, the largest lake in China, situated on the Qinghai-Tibet plateau. The study entailed detailed mapping of Hg sediment concentrations and a subsequent environmental risk assessment. Considering the complex nature of the plateau landform and surface vegetation, the study area was delineated at a 100 km radius centered on Qinghai Lake, which was divided into 30 sectors to quantify relationships between land use and the sediment Hg concentration. The results revealed a mean sediment Hg concentration of 29.91 μg/kg, which was elevated above the background level. Kendall's correlation analysis revealed significant but weak associations between sediment Hg concentrations and three land use types: grassland (rangeland and trees) (rs = 0.27, p < 0.05), crops (rs = −0.37, p < 0.05), and bare ground (rs = −0.25, p < 0.1), suggesting that growing areas of grassland correlated with higher Hg levels in the lake sediment, in contrast to bare ground or crops area, which correlated with lower Hg concentrations. Multiple linear regression models also observed weak negative relationships between bare ground and crops with sediment Hg concentration. This research methodology enhances our understanding of the impact of land use on Hg accumulation in lake sediments and underscores the need for integrated watershed management strategies to mitigate Hg pollution in Qinghai Lake.