Catchment Soils Research Articles

Soil ecological stoichiometry synchronously regulates stream nitrogen and phosphorus concentrations and ratios

Whether and how to synchronously regulate stream water nitrogen (N) and phosphorus (P) concentrations and ratios is a major challenge for sustainable aquatic functions. Soil carbon (C):N:P ratios influence soil N and P stocks and biogeochemical processes that elicit subsequent substantial impacts on stream water N and P concentrations and ratios. Therefore, bridging soil and stream water with ecological stoichiometry is one of the most promising technologies for improving stream water quality. Here, we quantified the ecological stoichiometry of soil and stream water relationships across nine catchments. Soil C:P ratio was the main driver of water quality, showing negative correlations with stream water N and P concentrations, and positive correlations with the N:P ratio in P-limited catchments. We revealed that soil C:P ratios higher than 97.8 mol mol−1 are required to achieve the simultaneous regulation of stream water N and P concentrations below the eutrophication threshold and make algal growth P-limited. Furthermore, we found that the relationships between catchment landscape and soil ecological stoichiometry likely provided practical options for regulating soil ecological stoichiometry. Our work highlights that soil ecological stoichiometry can effectively indicate the amount and proportion of soil N and P losses, and can be intervened through rational landscape planning to achieve sustainable aquatic ecosystems in catchments.

The impact of selected agrotechnical treatments on the growth of wild garlic (Allium ursinum L.) leaves in field cultivation

Wild garlic (Allium ursinum L.) is a typical spring geophyte whose natural habitat is beech forests. The research aimed to assess the possibility of cultivating wild garlic in field conditions significantly different from those required by this plant, using environmentally friendly and unconventional treatments. This study aimed to evaluate the effect of selected agricultural practices (catch crop, shading plant, biopreparations) on the growth of wild garlic leaves grown in the field. The results show that the biomass of catch crops and shade plants and biopreparations from marine algae are justified in cultivating wild garlic in field conditions regarding the leaf yield. Ploughing of phacelia biomass on a catchment soil with an unstable structure positively affected the growth of wild garlic, increasing the length of leaves, their number, and the length and width of the leaf blade. Winter turnip rape used as a shade plant caused an increase in the length of the leaves and the value of the FV/FM index (the quotient of the variable fluorescence to the maximum fluorescence), and also, depending on the year of the study, the length and width of the garlic leaf blade. Soaking the bulbs before planting in the ‘Kelpak SL’ solution increased the number of garlic leaves growing without turnip rape cover in the second and third years of cultivation. In the first year of vegetation, longer leaves with a larger leaf blade ensured the preparation was sprayed three times without pre-soaking the bulbs. Considering the biopreparations’ positive effect on the growth of garlic leaves and the FV/FM ratio values, their use is prospective regarding the increasing occurrence of dry years and is an alternative to plant irrigation.

Paleo-temperature inferred from brGDGTs over the past 18 cal ka BP from Lake Barrine, tropical NE Australia

Terrestrial temperature exerts a major influence on vegetation distribution, the hydrologic cycle and many biogeochemical cycles. Yet little research into terrestrial paleo-temperature reconstruction has been conducted covering the last deglaciation in northern Australia, and recent global surface temperature reconstructions include no data from this area. Here, for the first time, we reconstructed the mean annual air temperatures (MAAT) at Lake Barrine in this region from 18.3 to 1.7 cal ka BP at a relatively high resolution (averaged 400 yr). This temperature reconstruction was based on separated 5- and 6-methyl brGDGTs (branched glycerol dialkyl glycerol tetraethers) that are increasingly used to reconstruct terrestrial temperature because of their ubiquity and a preservation window of at least tens of millions of years. A 7.2 m master core from the center of the lake was extracted, along with five surface lake sediment and seven catchment soil samples. The results indicated that the fractional abundances of all the brGDGTs in the catchment soils, surface and downcore sediments in Lake Barrine were closely correlated, with dominant tetramethylated brGDGTs, especially Ia. We applied a global calibration to reconstruct the temperature using the lake sediment samples and a binary mixing model to correct temperature bias caused by soil-derived brGDGT input. The corrected temperature trend estimate compares favorably with the temperature anomaly recorded in the EPICA ice core record, except during the Younger Dryas. The corrected MAAT estimates at Lake Barrine indicated an increase across Heinrich Stadial 1 (HS 1; 18–14.9 cal ka BP) from 19.4 °C to 21.9 °C, a stable temperature during the Antarctic Cold Reversal (ACR; 14.7–13 cal ka BP) of ∼21.6 °C, followed by a slight decrease during the Younger Dryas (YD; 12.8–11.6 cal ka BP). After a further 1.6 °C increase into the early Holocene, the temperature decreased by 1.8 °C through the Holocene until a recent rise by 1.6 °C after 1.7 cal ka BP.

Application of an integrated catchment-lake model approach for simulating effects of climate change on lake inputs and biogeochemistry

Climate change is simultaneously affecting lakes and their catchments, resulting in altered runoff patterns in the catchment and modified mixing and biogeochemical dynamics in lakes. The effects of climate change in a catchment will eventually have an impact on the dynamics of a downstream water body as well. An integrated model would allow considering how changes in the watershed affect the lake, but coupled modelling studies are rare. In this study we integrate a catchment model (SWAT+) and a lake model (GOTM-WET) to obtain holistic predictions for Lake Erken, Sweden. Using five different global climate models, projections of climate, catchment loads and lake water quality for the mid and end of the 21st century have been obtained under two future scenarios (SSP 2-45 and SSP 5-85). Temperature, precipitation and evapotranspiration will increase in the future, overall resulting in an increase in water inflow to the lake. An increasing importance of surface runoff will also have consequences on the catchment soil, hydrologic flow paths, and the input of nutrients to the lake. In the lake, water temperatures will rise, leading to increased stratification and a drop in oxygen levels. Nitrate levels are predicted to remain unchanged, while phosphate and ammonium levels increase. A coupled catchment-lake configuration such as that illustrated here allows prediction of future biogeochemical conditions of a lake, including linking land use changes to changing lake conditions, as well as eutrophication and browning studies. Since climate affects both the lake and the catchment, simulations of climate change should ideally take into account both systems.

Trace Elements Contamination of Kilembe Copper Mine Catchment Soils in Kasese District, Western Uganda

ABSTRACT The mining and processing of copper in the Kilembe area, Western Uganda from 1956 to 1982 left behind several tailing sites containing cupriferous and coralliferous pyrites. A study was conducted to establish the concentrations of trace elements in point sources (tailings) within Kilembe mine and the distribution of trace elements within catchment soils. Mine tailings and catchment soils were sampled, acid digested and tested for elemental concentrations using ICP-MS. Tailings appeared to be the main sources of trace element contamination of soils with very high concentrations (mg kg−1) of Cu (240–11500), Co (101–180) and Ni (140–248) compared with average world crust concentration of Cu (20–75), Co (1–15) and Ni (20) mg kg−1. The concentration (mg kg−1) of Cu (3.5–975), Co (4.9–110) and Ni (5.3–180) in soils along the mine zone and downstream were significantly higher than upstream trace element concentrations and in many samples exceeding recommended agricultural thresholds. Positive and significant correlations were observed between Fe and Mn with all trace elements in soil, suggesting adsorption and co-precipitation processes. The major factors influencing trace element distributions in the soils were distances and locations relative to point sources of contaminants, with soils close to and downhill of tailing sites more contaminated with trace elements. Remediation of soils to reduce trace elements is recommended in addition to containment of tailing erosion.

PH drives the spatial variation of antibiotic resistance gene profiles in riparian soils at a watershed scale

Owing to convenient water access, riparian areas are often sites for intensive livestock breeding industries and agriculture, which can increase the spread of antibiotic resistance genes (ARGs). However, studies on ARG profiles in riparian soils are limited and there is little information regarding the factors influencing ARGs at a watershed scale. Here, we analyzed ARG profiles, bacterial communities, and soil properties in riparian soils under different land-use types. A total of 124 ARGs and 25 mobile genetic elements (MGEs) were detected in the riparian soils, which covered almost all major classes of antibiotics. Non-metric multidimensional scaling analysis showed that both the distance to the water reservoir and land-use types played important roles in shaping ARG profiles in riparian soils at a watershed scale. Downstream soils harbored three times the abundance of ARGs compared with upstream and midstream soils. Distance-decay analysis indicated that the similarity of ARG profiles and bacterial community composition decreased significantly with the increase of geographical distance (p < 0.001). When taking the land-use type into consideration, the relative abundance and diversity of ARGs and MGEs in orchard and farmland soils were significantly higher than those in wasteland soils. This indicated that anthropogenic activities can also affect ARG patterns in riparian soils. MGE abundance was identified as major driving factors of ARG profiles. In addition, among all the examined soil properties, soil pH was found to be more important than nutrients and organic carbon in shaping ARG profiles. Our findings provide valuable data on ARG distribution in riparian soils in a reservoir catchment and highlight downstream soils is crucial for ensuring water source security.

The role of earthquakes and storms in the fluvial export of terrestrial organic carbon along the eastern margin of the Tibetan plateau: A biomarker perspective

Driven by earthquakes and intense rainfall, steep tectonically active mountains are hotspots of terrestrial organic carbon mobilization from soils, rocks, and vegetation by landslides into rivers. Subsequent delivery and fluvial mobilization of organic carbon from different sources can impact atmospheric CO2 concentrations across a range of timescales. Extreme landslide triggering events can provide insight on processes and rates of carbon export. Here we used suspended sediment collected from 2005 to 2012 at the upper Min Jiang, a main tributary of the Yangtze River on the eastern margin of the Tibetan Plateau, to compare the erosion of terrestrial organic carbon before and after the 2008 Wenchuan earthquake and a storm-derived debris flow event in 2005. To constrain the source of riverine particulate organic carbon (POC), we quantified lignin phenols and n-alkanoic acids in the suspended sediments, catchment soils and landslide deposits. We found that riverine POC had higher inputs of less-degraded, discrete organic matter at high suspended sediment loads, while the source of POC seemed stochastic at low suspended sediment concentrations. The debris flow in 2005 mobilized a large amount of POC, resulting in an export of lignin within a single day equivalent to a normal year. In comparison, the 2008 Wenchuan earthquake increased the flux of POC and particulate lignin, albeit with limited impact on POC sources in comparison to seasonal variations. Our results highlight the important role of episodic events in the fluvial export of terrestrial carbon.

A new hydrological climatic proxy in arid lake sediments: Iodine‑uranium concentrations

Hydrological variation in the past ∼2 kyr is important for understanding the impact and driving forces of climate changes in the present and future, especially in arid areas. Sediment is one of the most useful archives in such a time period, and selection and validation of qualified hydrological proxies is the key point for reconstruction of hydrology in the past centuries. However, such research still faces a challenge due to limited knowledge of physiochemical implications of the traditional proxies in the specific lake, and difficulties to discriminate dry-wet from warm-cold signals. Here, a sediment core collected from Keluke Lake, Qaidam Basin, Northwest China was analyzed for iodine and uranium concentrations, to explore their potential as a new hydrological proxy in the arid regions for reconstructing the dry-wet changes during the past ∼2200 years. A significant correlation between iodine and uranium concentrations (r = 0.62, P < 0.01) was observed in the sediment core, and four peak events of synchronously varied iodine and uranium concentrations occurred in the studied sediment core. This indicates similar physiochemical behaviors of the two elements from the catchment to the sediments via lake water. During drier periods, as vegetation degradation and soil organic substance content decreased, water-soluble iodine and uranium were intensively leached, and fine particle associated iodine and uranium were seriously eroded from catchment soils. Meanwhile, the suspended matter concentrations and organic substance content in lake water increased as well, which facilitated more iodine and uranium to be deposited and recorded in the sediment as peak events. The four dry events coincide with the reported climatic changes in other lake sediments, ice core and aeolian sediments, and also correspond with the society evolution in this area, including the establishment of Tuyuhun Kingdom (313–663 CE), Tubo Empire (618–842 CE), Mongolian tribes (1495–1591 CE, and the Han population immigration driven by a severe drought disaster in 1876–1879.

Heavy metals and trace elements contamination risks in peri-urban agricultural soils in Nairobi city catchment, Kenya

IntroductionWith urbanization and industrialization in the developing world, urban and peri-urban agriculture is increasingly contributing to urban food systems, employment, and income generation opportunities. However, urbanization and industrialization may release harmful pollutants, including heavy metals and trace elements into agricultural soils, posing ecological, environmental and public health concerns. This paper assessed the potential risks of soil contamination with heavy metals and trace elements in peri-urban farmlands in Nairobi city catchment in Kenya. MethodsA total of 60 soil samples were collected from ten vegetable farming zones (S1-S10) and processed following standard protocols. The concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn were analyzed in the samples using inductively coupled plasma-mass spectrometry (ICP-MS). Results and discussionResults revealed that the soil samples have elevated concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn, with some elements including As (1.7%), Cd (13.3%), Mn (80%), Pb (1.7%) and Zn (11.7%) exceeding the permissible thresholds for agricultural soils. The spatial distribution of the elements exhibited three similar distribution patterns with slight variations between the hotspot sites of the different elements: (i) Co and Mn, (ii) Cu and Cr and (iii) As, Cd, Fe, Hg, Pb and Zn, while Ni and V exhibited singular spatial distributions compared to other elements. Elements such as As, Cd, Co, Fe, Hg, Mn, Pb and Zn appeared to be of anthropogenic enrichment, while Cr, Cu, Ni and V appeared to originate mainly from lithogenic and natural sources. The elements As, Cd, Hg and Pb exhibited high ecological risks, with Cd contributing about 46-66% of the overall ecological risk. The sampling sites S1, S5, S7, S9 and S10 depicted the highest ecological risks of 145, 103, 146, 121 and 146, respectively. The findings call for proper zoning of suitable agricultural areas and sound waste management protocols in urban and peri-urban landscapes. Further, remediation of contaminated soils and farmers’ sensitization are recommended for ecological and public health risk alleviation.

The Effect of Sediment Storage in Glaciated Catchments on Multimineral Detrital Geochronology: Deciphering Conflicting Zircon and Apatite U‐Pb Dates

AbstractDetrital geochronology and thermochronology are widely used to study erosion and the exhumation of rocks. In glaciated landscapes, these studies have shown exhumation to be highly heterogeneous; however, these studies have typically only applied apatite low‐temperature thermochronology, a mineral prone to mechanical and chemical breakdown, and a method with lower precision or data dispersion. As such, it is unclear if the detrital apatite signal represents derivation from the entire catchment. In this study, we present both zircon and apatite U‐Pb dates from a modern detrital sample of the Saco River, New Hampshire, USA. The river flows through a catchment that was highly modified during the last glacial maximum. The underlying geology is characterized by two contrasting groups from different eras; Palaeozoic metasediments and granites, and Mesozoic granitoids. Zircon U‐Pb dates are consistent with near‐uniform erosion of the catchment, encompassing both Proterozoic–Palaeozoic and Jurassic–Cretaceous grains consistent with the catchment's geology. However, detrital apatite U‐Pb dates are predominantly Palaeozoic. Detrital U‐Pb modeling shows that zircon grains are indeed derived from erosion of the entire catchment, while apatites likely originate from areas at high elevation. This stark contrast in ages likely indicates apatite's fragility. Dissolution resulting from acidic soils in the river's catchment is a likely cause, though mechanical breakdown during transport is also possible. As such, the detrital apatite signal appears to only record erosion from the modern fluvial system, while zircon represents a combination of uniform erosion during glaciation and the modern fluvial system. These findings imply the detrital apatite signal is prone to significant modification in areas of sediment storage and acidic soils with implications for sediment generation in other formerly glaciated landscapes worldwide.

Using stable water isotopes to evaluate water flow and nonpoint source pollutant contributions in three southern Ontario agricultural headwater streams

AbstractImproved understanding of catchment‐scale hydrology and nutrient transport in agricultural catchments is needed. Here, the annual young water fraction is determined for three southern Ontario headwater catchments using the stable water isotope δ18O; the dominant event contributions for three streams were also determined using a two‐component isotopic hydrograph separation. On an annual average, Nissouri Creek (loamy soils, high tile drainage) sees the lowest amount of event water, followed by Big Creek (clay soils, high tile drainage) and then North Creek (clay soils, low tile drainage). Event hydrograph separations show Nissouri Creek has significantly higher median amounts of pre‐event water than Big and North Creek during events. These results in indicate soil type may be more influential than tile drainage presence with respect to the contribution of event contributions to total stream flow; specifically, higher contributions of event water occurred in the two clay soil catchments, despite differing tile presence. Antecedent moisture and event characteristics did not uniformly explain the observed pre‐event water contributions for events across all sites, with pre‐event contributions only weakly and positively correlated with discharge at event commencement and negatively with isotopic variability in stream water. The total contribution of pre‐event water during events was significantly correlated with mean event turbidity and the flow‐weighted mean concentrations of dissolved organic carbon, total phosphorus and total dissolved phosphorus, but not total nitrogen or nitrate. The correlations we observed between pre‐event water and water chemistry were stronger than between event size and water chemistry, suggesting isotopic information adds insight that simple hydrometrics are unable to provide. Our results show that event water is responsible for phosphorus loss at the watershed scale, indicating actions targeting fast pathways or targeting pools of phosphorus available to those fast pathways can aid in reducing phosphorus transported by event water.

Biomarker-based quantitative constraints on maximal soil-derived brGDGTs in modern lake sediments

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are emerging as a powerful tool for quantifying past terrestrial temperature variations. In lake sediments, mixed lacustrine vs. soil sources of brGDGTs pose a challenge to quantitative application of this paleothermometer, and this effect has not yet been well-constrained. In this work, we analyzed concentrations and distributions of brGDGTs along with two other types of typical lipid biomarkers (isoGDGTs and long-chain n-alkanes) in modern sediments and catchment soils from 26 park lakes across a large climatic gradient in China. BrGDGTs in these lakes may largely represent the lacustrine signal due to the relatively small catchment area and high eutrophic condition. This is confirmed by the combined use of crenarchaeol, its isomer crenarchaeol′, and C33n-alkane as tracers of soil input for brGDGTs. This novel method quantifies the upper limit of soil brGDGT contribution to be less than 10% for most investigated lakes, with an average value of 7% ± 10%. Subsequently, the brGDGT signal of the assumed pure lacustrine origin was constrained by the subtle difference between the original sedimentary brGDGTs and those corrected by the maximum possible soil brGDGT input for those park lakes. A compilation of global freshwater lakes further shows that the correlation between the methylation index of brGDGTs (MBT or MBT′5ME) of their sediments and temperature matches that for the assumed pure lacustrine signals. Hence, soil contribution might be generally minor and may not significantly impact the quantitative application of the brGDGT paleothermometer for worldwide lakes. This study reinforces a foundation for this novel lacustrine paleothermometer to be applied in paleoclimate reconstructions, although factors affecting lacustrine brGDGT distributions within lakes still need to be better constrained.

Rainstorms drive export of aromatic and concurrent bio-labile organic matter to a large eutrophic lake and its major tributaries

Lakes are hotspots for global carbon cycling, yet few studies have explored how rainstorms alter the flux, composition, and bio-lability of dissolved organic matter (DOM) in inflowing rivers using high-frequency monitoring. We conducted extensive campaigns in the watershed of Lake Taihu and made daily observations for three years in its two largest inflowing tributaries, River Dapu and River Yincun. We found higher DOC, bio-labile DOC (BDOC), and specific UV absorbance (SUVA254) levels in the northwestern inflowing regions compared with the remaining lake regions. DOC and BDOC increased during rainstorms in River Dapu, and DOC declined due to local dilution and BDOC increased during rainstorms in River Yincun. We found that rainstorms resulted in increased DOM absorbance a350, SUVA254, and humification index (HIX) and enhanced percentages of humic-like fluorescent components, %polycyclic condensed aromatic and %polyphenolic compounds as revealed from ultrahigh-resolution mass spectrometry (FT-ICR MS), while spectral slope (S275-295) and the percentages of protein-like C1 and C3 declined during rainstorms compared with other seasons. This can be explained by a combined flushing of catchment soil organic matter and household effluents. The annual inflows of DOC and BDOC to Lake Taihu were 1.15 ± 0.18 × 104 t C yr−1 and 0.23 ± 0.06 × 104 t C yr−1 from River Dapu and 2.92 ± 0.42 × 103 t C yr−1 and 0.53 ± 0.07 × 103 t C yr−1 from River Yincun, respectively, and the fluxes of DOC and BDOC from both rivers increased during rainstorms. We found an elevated frequency of heavy rainfall and rainstorms in the lake watershed during the past six decades. We conclude that an elevated input of terrestrial organic-rich DOM with concurrent high aromaticity and high bio-lability from inflowing rivers is likely to occur in a future wetter climate.

Contrasting catchment soil pH and Fe concentrations influence DOM distribution and nutrient dynamics in freshwater systems

Organic matter (OM) quantity, quality, and nutrient dynamics within twelve shallow lakes in the Czech Republic were assessed in the context of catchment soil pH and iron (Fe) concentration. The catchments of the lakes were classified into two categories: (i) slightly acidic (soil pH = 5.1–6.3) with Fe-rich soils (H_Fe; Fe = 315–344 mg kg−1 in Mehlich 3 extract); and (ii) neutral (soil pH = 6.8–7.6) with Fe-poor soils (L_Fe; Fe = 126–259 mg kg−1 in Mehlich 3 extract). The quality of OM in the two lake types was characterized using a combination of spectroscopic techniques (UV–Vis, fluorescence, and Fourier Transform Infrared spectroscopy). We show that dissolved nutrient and dissolved organic carbon (DOC) concentrations, as well as the amount of aromatic and protein-like compounds in the water column and sediment porewater were significantly (p < 0.01) lower in the H_Fe lakes compared to the waterbodies located within L_Fe catchments. The FTIR analyses of the H_Fe sediments contained higher relative concentrations of aromatic compounds with hydroxyl-containing functional groups and carbohydrates, while more aliphatic and oxidised OM was found in the L_Fe lake sediments. These results suggest that the pH value of catchment soils and, particularly, their Fe content have profound geochemical effects on the mobility of OM and nutrients in the sediments of recipient waters. Because the OM-Fe association stabilises OM in sediments, waterbodies within L_Fe catchments are likely more vulnerable to increasing eutrophication and oxygen depletion compared to those in H_Fe catchments and this has important implications for water quality management, risk assessment, and predictions of aquatic ecosystem vulnerability under conditions of accelerating climate change.

Climate-related soil saturation and peatland development may have conditioned surface water brownification at a central European lake for millennia

Water brownification has long altered freshwater ecosystems across the northern hemisphere. The intensive surface water brownification of the last 30 years was however preceded by previous long-lasting more humic browning episodes in many catchments. To disentangle a cascade of browning-induced environmental stressors this longer temporal perspective is essential and can be reconstructed using paleolimnological investigations. Here we present a Holocene duration multi-proxy paleolimnological record from a small forest mountain lake in the Bohemian Forest (Czechia) and show that climate-related soil saturation and peatland development has driven surface water brownification for millennia there. A long core retrieved from the central part of the lake was dated using 14C and 210Pb, subsampled and analyzed for diatoms and zoological indicator (chironomids, planktonic cladocerans) remains. X-ray fluorescence (XRF) provided a record of elements sensitive to biogeochemical processes connected to browning and catchment development (P, Ti, Al/Rb, Fe/Ti, Mn/Ti, Si/Ti). Three threshold shifts related to the processes of water browning were detected in both diatom and chironomid successions at ~10.7, ~5.5 and ~4.2 cal. ky BP. Since, postglacial afforestation of the catchment ~10.7 cal. ky BP the lake experienced strong thermal stratification of the waters, but after ~6.8 cal. ky BP soil saturation and expansion of peatlands led to effective shading and probable nutrient limitation within the lake ecosystem. The more intensive in-wash of dissolved organic matter appears to decline after ~4.2 cal. ky BP, when the paludified catchment soils became permanently anoxic. Two temporary negative and positive anomalies of browning progress occur at the same time and may be connected with the “8.2 ka event” and the “4.2 ka event”, respectively. The key role of peatlands presence in the catchment was manifested in millennial-scaled browning process and a climatic forcing of long-lasting browning is evidenced by coincidence with the moistening of climate across the northern hemisphere after ~6 cal. ky BP.

Trophic Status of Shanti Sagara Reservoir: Implications on Nutrient Management in Reservoir Catchment

Water quality assessment of Shanti Sagara reservoir for drinking water supply and for water allocation to meet the demands in the semiarid climate is aimed. Seasonal water sampling (Pre monsoon, December 2021 &amp; Post monsoon, May 2022) at 2 depths to investigate physico-chemical parameters and assess the Water Quality index based on IS 10500: 2012 is found to be poor in pre monsoon, December 2021 and very poor in post monsoon, May 2022. Trophic status of the reservoir assessed based on Carlson’s Trophic State Classification (Secchi Depth, Total Nitrogen and Total Phosphorous) indicated that the reservoir is Hypereutrophic for Post Monsoon. This calls for assessment of internal nutrient load (silt characteristics) and external loading from the reservoir catchment (fertilizer from agriculture land) and the domestic water and the sewage water has contributed to high concentration of phosphorous (P) in Rudrapura and Jakli near Somalapura.&#x0D; Soil texture (sandy clay, silty loam, silty clay and sandy clay loam) in the reservoir catchment compliments high concentration of suspended sediment that increasers the turbidity in the reservoir. Turbidity present in the water alters the taste, colour and odour of the water and oxygen from the surface cannot be mixed to the bottom layer and oxygen is not released by photosynthesis in absence of light penetration (high turbidity levels) resulting in anoxic condition. Total Nitrogen (TN) in the catchment soil that contributes to the bottom of the reservoir is found to be high (201-217 kg/acre). Agriculture runoff in the month of (May, 2022) owing to precipitation results in high sediment concentration, that contributes to high nitrogen levels in the reservoir.&#x0D; Nutrients in suspended Sediments that have entered the reservoir altered the nutrient cycle in the reservoir ecosystem. High nutrient concentration in the silt characteristics i,e total nitrogen (159-168 kg/acre) and phosphorous (10.1-13.4 kg/acre) is due to stratification caused do level to low in hypolimnion layer and anoxic condition during summer resulting in growth of Phytoplankton the eutrophication. The suggested nutrient management strategies for the reservoirs catchment are optimizing nutrient application to the crop land, microbial water treatment before supplying it for drinking purpose, soil conservation structures in the reservoir catchment to restrict sediment entry to the reservoir and sewage treatment plant for the rural settlement.

English

Majority of people in rural areas of Uganda and other malaria-endemic parts of the world use medicinal plants to treat the disease. This study documented medicinal plants used to treat malaria around Kilembe copper mines and assessed the presence of essential and potentially toxic elements. Household surveys and key informant interviews were carried out while anti-malarial plants were sampled, prepared and concentrations of Fe, Mn, Zn, Co, Cu and Ni determined by atomic absorption spectrometry. It was established that Vernonia amygdalina (40%), Ocimum suave (35%), Justicia betonica (32%) and Aloe felox (20%) were the most used plants to treat malaria. Leaves were the most commonly used plant part (83%) while decoctions were reported by 51% of respondents. Concentration of trace elements (mg/kg) in the four plant species ranged from 50.4-422 (Mn), 16.7-202 (Fe), and 19.6-198 (Zn) and from 1.6-44.1, 0-7, and 0.1-31.5 for Cu, Co and Ni, respectively. Fe, Cu and Ni exceeded the recommended thresholds in almost all&nbsp; Kilembe&nbsp; mine samples&nbsp; as&nbsp; well&nbsp; as&nbsp; controls while Mn, Zn and Co exceeded thresholds in more&nbsp; than&nbsp; 25% of&nbsp; the samples. Remediation of Kilembe catchment soils as well as public sensitisation on the safety of medicinal plants is recommended. &nbsp; Key words: Malaria, medicinal plants, trace elements, Kilembe mine.

Geochemical accumulation and source tracing of heavy metals in arable soils from a black shale catchment, southwestern China

Heavy metal enrichment in soils has been linked to the weathering of lithologies with high geochemical backgrounds, such as black shale. Therefore, this study conducted a typical sampling of surface soils in a black shale catchment in southwestern China to characterize the accumulation and sources of the heavy metals As, Cd, Co, Cr, Cu, Ni, Pb, Zn, Mo and Tl. Elevated concentrations of most heavy metals in the soils underlain by black shale are determined to exceed the regional soil background values, even the risk screening values, especially for Mo, As and Cd. Sequential extraction analysis, together with previous results, reveals that most heavy metals in soils are mainly bound in the residual fraction (> 65 %) as a result of the fixation of stable aluminosilicates (e.g., clay minerals). In contrast, Cd mainly occurs in relatively labile proportions as exchangeable (24.42 %), carbonate (24.48 %) and Fe/Mn oxide fractions (26.60 %) due to the non-specific adsorption of soil colloids and the precipitation of carbonates and Fe/Mn oxides. Pb isotopic tracing and APCS/MLR receptor model suggest that heavy metals in the urban surface soils (SG1) have a mixed source of black shale weathering, vehicle exhaust and agricultural input, while heavy metals in the rural surface soils (SG2) are a geogenic source of black shale weathering. Overall, this study provides new insights into contamination management, land use planning and health risk assessment in regions with high geochemical backgrounds.

Eutrophication has a greater influence on floodplain lake carbon cycling than dam installation across the middle Yangtze region

Carbon cycling in shallow floodplain lakes is complex due to variability in delivery of flood-derived allochthonous organic matter (OM). Human activities have potential to significantly modify the carbon balance of lakes by damming which restricts external OM inputs and via eutrophication which can increase the in-lake production of algae and/or aquatic plants. In order to understand how these human activities influence carbon cycling in shallow floodplain lakes over decadal-centennial timescales, we analysed C/N ratios and δ13C from terrestrial plants, catchment soils, aquatic plants and dated sediment cores from six heavily modified lakes in the middle Yangtze floodplain. Submerged macrophytes (−21.4 ± 4.6 ‰) had higher δ13C than C3 plants from the catchment (−26.6 ± 0.6 ‰) and emergent and floating plants (−26.6 ± 4.0 ‰). Increases in sedimentary chlorophyll a (from primary producers) were associated with a decline in sedimentary δ13C in the severely eutrophic Dongting, Luhu, Wanghu and Poyang Lakes after the 1980s. In contrast, sedimentary δ13C increased in Honghu and Futou Lakes which have abundant submerged macrophytes. The timing and scale of sedimentary δ13C changes indicated stronger responses to eutrophication than damming, with eutrophication responses ranging from a macrophyte proliferation to the dominance of phytoplankton.

The Influence of the Degree of Forest Management on Methylmercury and the Composition of Microbial Communities in the Sediments of Boreal Drainage Ditches.

Inorganic mercury (Hg) can be methylated to the highly toxic and bioavailable methylmercury (MeHg) by microorganisms in anaerobic environments. The Hg methylation rate may be affected by forest management activities, which can influence the catchment soils, water, and sediments. Here, we investigate the influence of forest management in the form of ditch cleaning and beaver dam removal, as well as the seasonal variations, on sediment chemistry and microbiota. The relationships between MeHg concentrations in sediment samples and archaeal and bacterial communities assessed by 16S rRNA gene amplicon sequencing were investigated to determine the microbial conditions that facilitated the formation of MeHg. Concentrations of MeHg were highest in undisturbed catchments compared to disturbed or slightly disturbed sites. The undisturbed sites also had the highest microbial diversity, which may have facilitated the formation of MeHg. Low MeHg concentrations and microbial diversity were observed in disturbed sites, which may be due to the removal of organic sediment layers during ditch cleaning and beaver dam removal, resulting in more homogenous, mineral-rich environments with less microbial activity. MeHg concentrations were higher in summer and autumn compared to winter and spring, but the temporal variation in the composition and diversity of the microbial community was less than the spatial variation between sites. Beta diversity was more affected by the environment than alpha diversity. The MeHg concentrations in the sediment were positively correlated to several taxa, including Cyanobacteria, Proteobacteria, Desulfobacterota, Chloroflexi, and Bacteroidota, which could represent either Hg-methylating microbes or the growth substrates of Hg-methylating microbes.