Tonnes Yr Research Articles

The mid-transition in the electricity sector: impacts of growing wind and solar electricity on generation costs and natural gas generation in Alberta

In response to climate change, electricity grids are decreasing their carbon intensity with the addition of wind and solar variable renewable energy generation (VREN). This leads to a mid-transition period, where renewable energy is unable to satisfy electricity demand without contributions from other fossil sources such as natural gas, but also generates sufficiently to constrain conventional generation—changing their operating and market conditions. We use a simplified copper plate model, which scales up and down historical wind and solar generation, to examine how and when the patterns and generation costs for fossil fuel power could change by the increasing capacities of VREN on the relatively isolated Alberta electricity grid. We find that beginning at 20% VREN an increasingly diverse range and reduced hours of dispatched capacity is necessitated from the existing generation. However, even as capacity factors for fossil fuel generation decrease their costs remain reasonable and we found this to be a low-cost pathway for achieving moderate to deep emission reduction goals. A full 86% of demand could be met with VREN before generation costs exceeded 100$/MWh, allowing for an emissions reduction of 28.4–9 million tonnes yr−1 of CO2eq, on a lifecycle basis. In order to integrate the renewable generation, new and existing fossil fuel units will require market rules that incentivise flexibility and ensure they remain in place throughout the transitionary period as they are crucial to balance variable renewable generation.

Estimating the Global Influence of Cover Crops on Ecosystem Service Indicators in Croplands With the LPJ‐GUESS Model

AbstractCover crops (CCs) can improve soil nutrient retention and crop production while providing climate change mitigation co‐benefits. However, quantifying these ecosystem services across global agricultural lands remains inadequate. Here, we assess how the use of herbaceous CCs with and without biological nitrogen (N) fixation affects agricultural soil carbon stocks, N leaching, and crop yields, using the dynamic global vegetation model LPJ‐GUESS. The model performance is evaluated with observations from worldwide field trials and modeled output further compared against previously published large‐scale estimates. LPJ‐GUESS broadly captures the enhanced soil carbon, reduced N leaching, and yield changes that are observed in the field. Globally, we found that combining N‐fixing CCs with no‐tillage technique could potentially increase soil carbon levels by 7% (+0.32 Pg C yr−1 in global croplands) while reducing N leaching loss by 41% (−7.3 Tg N yr−1) compared with fallow controls after 36 years of simulation since 2015. This integrated practice is accompanied by a 2% of increase in total crop production (+37 million tonnes yr−1 including wheat, maize, rice, and soybean) in the last decade of the simulation. The identified effects of CCs on crop productivity vary widely among main crop types and N fertilizer applications, with small yield changes found in soybean systems and highly fertilized agricultural soils. Our results demonstrate the possibility of conservation agriculture when targeting long‐term environmental sustainability without compromising crop production in global croplands.

Renewable energy solutions based on artificial intelligence for farms in the state of Minas Gerais, Brazil: Analysis and proposition

Rural areas have great renewable energy potential. With an introduction to sustainable development goals, the smart farm concept presents a novel idea for providing energy in rural areas using artificial intelligence and renewable energy management. We proposed the following topics in this research: (i) methodologies for sizing generation systems by integer linear programming, (ii) use of analytic hierarchy process (AHP) to select the alternative source by financial, environmental, social, and physical criteria, and (iii) training of an artificial neural network (ANN) for process optimization based on the agroeconomic profile of farms. We applied the proposed generic methodology to farms in São Francisco do Glória, Brazil. The biomass, solar, and wind systems were indicated by AHP for implementation in 62.16, 15.32, and 22.52% of farms, respectively. The best configuration of ANN presented a maximum precision of 81.80 ± 3.36%. If the systems were to be implemented, 1.975 GWh yr−1 would be generated, 435.23 tonnes of CO2 would no longer be emitted per year, and a CO2 credit of 366.62 tonnes yr−1 would be injected into the national electric system. Public policies are necessary for this scenario to become a reality in Brazil, such as research incentives and market development.

Spatially consistent microbial biomass and future cellular carbon release from melting Northern Hemisphere glacier surfaces

Melting glacier ice surfaces host active microbial communities that enhance glacial melt, contribute to biogeochemical cycling, and nourish downstream ecosystems; but these communities remain poorly characterised. Over the coming decades, the forecast ‘peak melt’ of Earth’s glaciers necessitates an improvement in understanding the state and fate of supraglacial ecosystems to better predict the effects of climate change upon glacial surfaces and catchment biogeochemistry. Here we show a regionally consistent mean microbial abundance of 104 cells mL−1 in surface meltwaters from eight glaciers across Europe and North America, and two sites in western Greenland. Microbial abundance is correlated with suspended sediment concentration, but not with ice surface hydraulic properties. We forecast that release of these microbes from surfaces under a medium carbon emission scenario (RCP 4.5) will deliver 2.9 × 1022 cells yr−1, equivalent to 0.65 million tonnes yr−1 of cellular carbon, to downstream ecosystems over the next ~80 years.

Natural and anthropogenic effects on spatio-temporal variation in sediment load and yield in the Godavari basin, India

River sediment, the most crucial component of the land-ocean interaction, is enduring substantial changes worldwide because of anthropogenic alterations and climate change. Our study assesses the interaction of sediment load variability and yield to the rainfall, land-use, and dam constructions at both spatial and temporal scales in the Godavari and its major tributaries. The most important river basin in Peninsular India, the Godavari, has witnessed a dramatic decline (p-value <0.001) in sediment load over the past five decades, with average annual rates of 2 million tonnes (Mt) yr−1. Sediment load in the Godavari reduced from 150 Mt between 1970 and 1979, to 115 Mt in 1980–1989, 98 Mt in 1990–1999, 48 Mt in 2000–2009, and 47 Mt in 2010–2019, respectively. While sediment load in the Godavari and its major tributaries is declining significantly, the rainfall showed an overall insignificant increasing trend barring the Sabari sub-catchment, where the rainfall is increasing at a significant rate of 7 mm yr−1 (p-value = 0.001). Twenty-five sub-basins in the Godavari showed a large variation in sediment yield (28 to 3404 t km−2 yr−1). Our results revealed that spatial variability in sediment yield is primarily associated with both rainfall and land-use pattern. The temporal variation in sediment load in the Godavari and Pranhita is associated with intensified human activities during the most recent decades, while climate is the primary controlling factor in Indravati and Sabari sub-catchments. Sediment entrapment under a high rate of siltation by reservoirs in the Godavari has sharply reduced the sediment flux to the Bay of Bengal, causing aggravated delta erosion by wave actions. The findings of this study have significant implications for understanding the complex interrelationship between the management of reservoirs, land use, sediment loads, denudation, and coastal erosion in the Godavari catchment.

Can plant or lichen natural abundance 15N ratios indicate the influence of oil sands N emissions on bogs?

Study regionThe 140,329 km2 Athabasca Oil Sands Administrative Area (OSAA), which contains 8982 km2 of bogs. Since the late 1970s, N emissions from oil sands development in the OSAA have steadily increased, reaching over 80,000 metric tonnes yr−1 in 2017. Study focusIf oil sands N emissions have distinct stable isotopic signatures, it may be possible to quantify the extent to which these emissions have affected N cycling in surrounding aquatic, wetland, and terrestrial ecosystems. To assess the potential for 15N as a tracer of oil sands N emissions, we measured natural abundance 15N ratios and tissue N concentrations in 10 plant or lichen species at 6 peatland sites at different distances from the oil sands region, collected on 17 sampling dates over three years (2009–2011). New hydrological insightsTo understand how the pressures of changing N and S deposition regimes and hydrologic disturbance interactively affect the region’s wetlands, it is critical to understand how these pressures act individually. The epiphytic lichen, Evernia mesomorpha, was the only species that exhibited patterns that could be interpreted as being influenced by oil sands N emissions. The paucity of data on δ15N signatures of oil sands related N sources precludes definitive interpretations of δ15N in plant or lichen tissues with respect to oil sands N emissions.

Optimized continuous-thrust round-trip trajectories to ultra-low Δv ISRU targets

We present the results and implications of our optimized round-trip trajectories to thousands of synthetic but realistic ultra-low Δv (≲ 8 ​km ​s−1) asteroids for the purpose of in-space resource utilization (ISRU) of water extracted from the targets. We show that our carpe diem mission scenario works — ISRU missions utilizing ‘hibernating’ spacecraft on loosely-bound orbits in cis-lunar space can begin soon after targets are discovered if the asteroids are rapidly characterized with accurate and precise orbits. Our algorithm identified ultra-low Δv round-trip mission trajectories for 100% of the ISRU targets that approach to within 0.05 au of Earth. The median minimum distance between the targets and Earth during the rendezvous/mining phase is ∼ 0.23 au (∼ 115 light-seconds) while the maximum one-way communication time is ​≲ ​4 ​min. The return-trip missions have a median Δv ∼ 2.9 ​km ​s−1 so that the typical mission returns about 50% of the extracted H2O to cis-lunar space. We estimate a steady-state rate of about 2 water-mining missions per year returning about 100 tonne yr−1 to the Earth-Moon system. Converting the water to LOX/LH2 is ∼ 93% efficient, suggesting that asteroid H2O mining could provide ∼ 93 tonne of bipropellant to cis-lunar space on an annual basis. We applied our mission optimization algorithm to 168 known near-Earth objects (NEO) with orbital elements similar to our synthetic ultra-low Δv population and estimate that almost 95% of the population of ultra-low Δv NEOs remain to be discovered.

Potential land microalgae cultivation in Mexico: From food production to biofuels

A geographic information system model was built to identify the areas in Mexico with high potential for microalgae production. The input data was obtained from diverse national and international sources. The model was constructed using multiple criteria for facility siting, including the following land characteristics and resources: land use, topographic slope, temperature, evaporation, solar radiation, vegetation, water and CO2 sources, wastewater treatment plants, rivers and lakes, cities and roads, natural protected areas, historical sites, Ramsar sites, airport locations and geological faults. Various models were constructed by assigning weights according to suitability to the data layers. Suitable areas for microalgae production were identified in up to 26.8% of the country, equivalent to 526,672 km2. Specifically, the states of Jalisco, Oaxaca and Veracruz had the largest areas suitable for microalgae cultivation, with a potential production of around 9 million Tonnes yr−1 of dry biomass, representing the feasibility of microalgae production in the country.

Marine microalgae commercial production improves sustainability of global fisheries and aquaculture

A method is described for saving 30% of the world fish catch by producing fishmeal and fish oil replacement products from marine microalgae, the natural source of proteins and oils in the marine food web. To examine the commercial aspects of such a method, we adapt a model based on results of microalgae production in Hawaii and apply it to Thailand, the world’s fourth largest producer of fishmeal. A model facility of 111 ha would produce 2,750 tonnes yr−1 of protein and 2,330 tonnes yr−1 of algal oil, at a capital cost of $29.3 M. Such a facility would generate $5.5 M in average annual net income over its 30-year lifetime. Deployment of 100 such facilities in Thailand would replace all domestic production of fishmeal, 10% of world production, on ~1.5% of the land now used to cultivate oil palm. Such a global industry would generate ~$6.5 billion in annual net income.

Estimation of packaged water consumption and associated plastic waste production from household budget surveys

Packaged water consumption is growing in low- and middle-income countries, but the magnitude of this phenomenon and its environmental consequences remain unclear. This study aims to quantify both the volumes of packaged water consumed relative to household water requirements and associated plastic waste generated for three West African case study countries. Data from household expenditure surveys for Ghana, Nigeria and Liberia were used to estimate the volumes of packaged water consumed and thereby quantify plastic waste generated in households with and without solid waste disposal facilities. In Ghana, Nigeria and Liberia respectively, 11.3 (95% confidence interval: 10.3–12.4), 10.1 (7.5–12.5), and 0.38 (0.31–0.45) Ml day−1 of sachet water were consumed. This generated over 28 000 tonnes yr−1 of plastic waste, of which 20%, 63% and 57% was among households lacking formal waste disposal facilities in Ghana, Nigeria and Liberia respectively. Reported packaged water consumption provided sufficient water to meet daily household drinking-water requirements for 8.4%, less than 1% and 1.6% of households in Ghana, Nigeria and Liberia respectively. These findings quantify packaged water’s contribution to household water needs in our study countries, particularly Ghana, but indicate significant subsequent environmental repercussions.

Estimation of soil erosion rate in the Democratic People's Republic of Korea using the RUSLE model

ABSTRACTForests are well known to control soil erosion and severe flooding. In the Democratic People's Republic of Korea (North Korea), deforestation was estimated at 20% between 1997 and 2014. This decline was mainly reflective of improper land use practices on steep slopes. Intensive deforestation and inappropriate land management can lead to severe soil erosion. The objective of this study was to describe the regional soil erosion severity in North Korea using the Revised Universal Soil Loss Equation (RUSLE) model coupled with a GIS technique. This model is widely being used to assess the potential mean annual soil erosion under different rainfall, soil characteristics, slope, and land use conditions. The results showed that the average annual rate of soil loss was estimated to be 15.8 tonnes ha−1 yr−1. Regionally, Nampo city is the most vulnerable region to soil erosion (55.1 tonnes ha−1 yr−1), followed by Hwanghaebuk-do (30.5 tonnes ha−1 yr−1), due to rapid land development. Denuded lands, which are estimated at around 6.5% of the total area, are predicted to have contributed 192.1 million tonnes yr−1 to the country's soil erosion. Participatory agroforestry and reforestation were found to be practical solutions to reduce soil erosion, particularly on degraded landscapes, and improve people's farm-based livelihoods.

Multiple land use activities drive riverine salinization in a large, semi‐arid river basin in western Canada

AbstractSalinization is increasingly recognized as a global issue. However, the relative importance of different drivers across a broad range of ions and ecosystems is not well understood. This study examined spatial and temporal dynamics in riverine salinity (conductivity, Ca2+, Mg2+, Na+, K+, , Cl− and ) in the South Saskatchewan River Basin (SSRB), a semi‐arid, mixed land use watershed in Alberta, Canada. A significant temporal increase (p &lt; 0.05) in the concentration of one or more ions was observed at all 12 study sites. While all ions exhibited a significant increase in concentration over time, the rate of change was generally highest for Cl− (≈ 1.4–3.0% yr−1). The observed increase in riverine Cl− loading downstream of a large urban center (≈ 1700 tonnes yr−1) was attributed to increasing inputs from road salt (≈ 1800 tonnes yr−1) and to a lesser extent municipal wastewater (≈ 400 tonnes yr−1). For most other salts, spatial variation was driven not by urbanization but by the proportion of salt affected soils and/or cropland. A distinct Na2SO4 signal was observed at stations draining salt affected soils which strengthened over time at 7/12 sites indicating temporal trends in Na+ and have been driven largely by soil processes. A strong relationship between cropland and salt chemistry across the basin suggests agricultural activities have also contributed to observed trends. Therefore, in regions with similar climatic and anthropogenic characteristics to the SSRB, multiple stressors are likely to be operating and as such, these systems may be at particular risk from salinization.

Ecosystem services from southern African woodlands and their future under global change.

Miombo and mopane woodlands are the dominant land cover in southern Africa. Ecosystem services from these woodlands support the livelihoods of 100 M rural people and 50 M urban dwellers, and others beyond the region. Provisioning services contribute $9 ± 2 billion yr−1 to rural livelihoods; 76% of energy used in the region is derived from woodlands; and traded woodfuels have an annual value of $780 M. Woodlands support much of the region's agriculture through transfers of nutrients to fields and shifting cultivation. Woodlands store 18–24 PgC carbon, and harbour a unique and diverse flora and fauna that provides spiritual succour and attracts tourists. Longstanding processes that will impact service provision are the expansion of croplands (0.1 M km2; 2000–2014), harvesting of woodfuels (93 M tonnes yr−1) and changing access arrangements. Novel, exogenous changes include large-scale land acquisitions (0.07 M km2; 2000–2015), climate change and rising CO2. The net ecological response to these changes is poorly constrained, as they act in different directions, and differentially on trees and grasses, leading to uncertainty in future service provision. Land-use change and socio-political dynamics are likely to be dominant forces of change in the short term, but important land-use dynamics remain unquantified.This article is part of the themed issue ‘Tropical grassy biomes: linking ecology, human use and conservation’.

Is Ongoing Sulfluramid Use in South America a Significant Source of Perfluorooctanesulfonate (PFOS)? Production Inventories, Environmental Fate, and Local Occurrence

Despite international phase-out initiatives, production and use of perfluorooctanesulfonate (PFOS) and related substances continues in some countries. In Brazil, the PFOS-precursor N-ethyl perfluorooctane sulfonamide (EtFOSA) is used in Sulfluramid, a pesticide for controlling leaf-cutting ants. New data on production, environmental fate, and occurrence of Brazilian Sulfluramid are reported herein. From 2003 to 2013, Brazilian Sulfluramid manufacturing increased from 30 to 60 tonnes yr(-1) EtFOSA. During this time <1.3 tonnes yr(-1) were imported, while exports increased from ∼0.3 to 2 tonnes yr(-1). From 2004 to 2015, most EtFOSA was exported to Argentina (7.2 tonnes), Colombia (2.07 tonnes), Costa Rica (1.13 tonnes), Equador (2.16 tonnes), and Venezuela (2.4 tonnes). Within Brazil, sales occurred primarily in the states of Minas Gerais, São Paulo, Mato Grosso do Sul, Espírito Santo, and Bahia. Model simulations predict EtFOSA will partition to soils, while transformation products perfluorooctane sulfonamide (FOSA) and PFOS are sufficiently mobile to leach into surface waters. In support of these predictions, up to 3400 pg L(-1) of FOSA and up to 1100 pg L(-1) of PFOS were measured in Brazilian surface water, while EtFOSA was not detected. The high FOSA/PFOS ratio observed here (up to 14:1) is unprecedented in the scientific literature to our knowledge. Depending on the extent of conversion of EtFOSA, cumulative Brazilian Sulfluramid production and import from 2004 to 2015 may contribute between 167 and 487 tonnes of PFOS/FOSA to the environment. These levels are clearly nontrivial and of concern since production is continuing unabated.

Benthic dissolved organic carbon fluxes in a drinking water reservoir

The trend of increasing dissolved organic carbon (DOC) in surface waters motivated us to gain a mechanistic understanding of DOC exchange at the sediment water interface in lakes. We quantified seasonal DOC and solute fluxes under different redox conditions, in a small drinking water reservoir using sediment core incubations. Processes governing benthic DOC exchange were microbial production of DOC and interaction with mineral surfaces. Mobilization of DOC in anoxic sediments seemed to be closely linked to reductive dissolution of ferric minerals as shown by the strong positive correlation (r2 = 0.99) between DOC and Fe fluxes. Oxidized surface sediments were an efficient DOC trap where DOC was bound to ferric minerals. Redox conditions appeared to be the primary regulator of the DOC exchange, resulting in sedimentary uptake of DOC (−1.8 mmol m−2 d−1) only under oxic conditions. DOC production was regulated by temperature, leading to higher DOC fluxes (up to 2.4 mmol m−2 d−1) in summer. The sediment was a net sink of DOC (−0.2 tonnes yr−1) but this was small compared with the annual DOC load (15 tonnes yr−1) of the reservoir. However, the benthic DOC flux was about 10–20% of the dissolved carbon flux at the sediment–water interface, making it a significant process in the lake internal carbon cycle. Climate change is supposed to promote reducing conditions at the bottom of lakes, which might increase benthic DOC production in the future.

A model for the future: Ecosystem services provided by the aquaculture activities of Veta la Palma, Southern Spain

Abstract The lack of space and opportunity for development has been identified as key reasons behind the stagnation of the European aquaculture industry. With the historical loss and degradation of current European wetlands there is an opportunity for harnessing the commercial investment of the aquaculture industry in construction of dual purpose wetlands that incorporate both conservation and extensive aquaculture activities. These wetlands can be used to expand the area available to suitable aquaculture into ecologically sensitive areas, such as Natura 2000 sites. Veta la Palma (VLP) situated in the Donana Natural Park (and a Natura 2000 site) is an example of such an aquaculture development and a possible model for future opportunities. In the current study some of the important ecosystem services that are provided by VLP are assessed. The provisioning services of VLP were the economic rationale for the investment and more than 820 tonnes yr − 1 of fish and shrimp is produced, through a mixture of semi-extensive and extensive aquaculture. The regulating services include nutrient absorption, and the flow of river water through VLP and high primary production results in the absorption of 377 tonnes of dissolved inorganic nitrogen yr − 1 , and 516 tonnes of C yr − 1 . Supporting services include the provision of habitat for more than 94 bird and 21 fish species. The primary production that supports the birds, extensive and semi-extensive aquaculture production was also estimated to be 167,000 tonnes, 50,000 tonnes and 133,000 tonnes yr − 1 , respectively. The losses to birds are substantial and these estimates indicate that almost half of the primary production supports the wetland birds which directly consume 249 tonnes of fish and 2578 tonnes of invertebrates per annum. However it is the ecological credentials of the farm that enable premium prices and hence ensure the economic viability of the farm. The study demonstrates the possibility of using aquaculture to mitigate the historical loss of wetlands, provide significant ecosystem services and contribute to achievement of the European environmental legislative goals, and furthers the opportunity for the expansion of aquaculture into sensitive but impacted habitats. Statement of relevance Demonstrates potential environmental benefits of aquaculture.

Examination of the role of dreissenids and macrophytes in the phosphorus dynamics of Lake Simcoe, Ontario, Canada

Our study examines the relative importance of the causal linkages between exogenous total phosphorus (TP) loading and internal nutrient recycling with the water quality conditions in Lake Simcoe, Ontario, Canada. We enhance the mechanistic foundation of a simple TP mass-balance model, originally developed to guide the eutrophication management in the system. The structural improvements include the incorporation of macrophyte dynamics, the explicit representation of the role of dreissenids in the system, and the improved portrayal of the interplay between water column and sediments. Our model provides good agreement with the observed TP variability in the system during the study period (1999–2007). Consistent with empirical evidence, our model predicts that macrophyte uptake from the interstitial waters is responsible for a significant loss of P from the sediments. Our model also suggests that dreissenids filter a considerable amount of particulate P from the water column, but the effective clearance rate is significantly lower with a substantial amount of the filtered particles (>85%) returned into the water column as faeces, pseudofeces or other metabolic excreta. P diffusive fluxes from the sediments account for about 30–35% of the exogenous P loading in Lake Simcoe. The sediments in the main basin are mostly driven by fast diagenetic processes of settling organic matter from the epilimnion, suggesting an internal P loading of 9.2tonnes yr−1. Finally, our study attempts to explain the lack of distinct decreasing trends in ice-free TP concentrations after the invasion of dreissenid mussels, suggesting that the presence of active nutrient recycling pathways, potentially magnified by the particular morphological features and hydrodynamic patterns of Lake Simcoe, could counterbalance the direct effects of dreissenid filtration.

Kerogen maturation data in the Uinta Basin, Utah, USA, constrain predictions of natural hydrocarbon seepage into the atmosphere

Natural seepage of methane from the lithosphere to the atmosphere occurs in regions with large natural gas deposits. According to some authors, it accounts for roughly 5% of the global methane budget. I explore a new approach to estimate methane fluxes based on the maturation of kerogen, which is the hydrocarbon polymer present in petroleum source rocks and whose decomposition leads to the formation of oil and natural gas. The temporal change in the atomic H/C ratio of kerogen lets us estimate the total carbon mass released by it in the form of oil and natural gas. Then the time interval of active kerogen decomposition lets us estimate the average annual formation rate of oil and natural gas in any given petroleum system, which I demonstrate here using the Uinta Basin of eastern Utah as an example. Obviously, this is an upper bound to the average annual rate at which natural gas seeps into the atmosphere. After adjusting for biooxidation of natural gas, I conclude that the average annual seepage rate in the Uinta Basin is not greater than (3100 ± 900) tonne yr−1. This is (0.5 ± 0.15)% of the total flux of methane into the atmosphere over the Basin, as measured during aircraft flights. I speculate about the difference between the regional 0.5% and the global 5% estimates.

Assessing dam pool sediment for understanding past, present and future watershed dynamics: An example from the Cuyahoga River, Ohio

Abstract Dams can trap a stream's sediment load and create a sediment record of anthropogenic watershed impacts and stream sediment load variability. We demonstrate the usefulness of dam pool sediments in assessing past, present, and future watershed dynamics in this study of the Gorge Dam Pool, Cuyahoga River, Ohio. The 17.4-m-tall Gorge Dam was constructed in 1912 and subsequently trapped the sediment load of the Middle Cuyahoga River. 210 Pb dating of the impoundment sediment allowed past anthropogenic impacts to be assessed. Mud accumulating between 1912 and 1926 has high trace metal content from industrial activities upstream of the impoundment. Between 1926 and 1978 mud having abundant coal combustion products (CCP) and high but variable metal content accumulated. During this period, sediment accumulation increased due to urbanization in the watershed. Since 1978 CCP and trace metals decline, reflecting the effectiveness of environmental regulations. Sediment accumulation increased dramatically between 2004 and 2008 and again in 2011 as a result of increased extreme flow events. An impoundment sediment accumulation of 7520 tonnes yr −1 for the 210 Pb-dated year 2006 is similar to a watershed model estimate of 7490 tonnes yr −1 determined from year 2006 landcover and supports the use of watershed modeling to estimate sediment load. Dam removal to reestablish river connectivity also eliminates the impoundment sediment trap. The impoundment sediment load record allows for a projection to the downstream sediment load following dam removal. The potential removal of the Gorge Dam will result in a minimal increase to the Lower Cuyahoga River sediment load.

Assessing ways to combat eutrophication in a Chinese drinking water reservoir using SWAT

Across China, nutrient losses associated with agricultural production and domestic sewage have triggered eutrophication, and local managers are challenged to comply with drinking water quality requirements. Evidently, the improvement of water quality should be targeted holistically and encompass both point sources and surface activities within the watershed of a reservoir. We expanded the ordinary Soil Water Assessment Tool – (SWAT) with a widely used empirical equation to estimate total phosphorus (TP) concentrations in lakes and reservoirs. Subsequently, we examined the effects of changes in land and livestock management and sewage treatment on nutrient export and derived consequences for water quality in the Chinese subtropical Kaiping (Dashahe) drinking water reservoir (supplying 0.4 million people). The critical load of TP was estimated to 13.5 tonnes yr–1 in order to comply with the minimum drinking water requirements, which corresponds to 87% of the simulated load to the reservoir at present. Both the implementation of buffer zones along rivers and removal of sewage discharges showed marked improvement in reservoir water quality. Future research should focus on both hydrological model performance and nutrient transport pathways, which are challenged by a complex artificially altered water infrastructure in the form of ditches, channels and ponds in monsoon-influenced subtropical watersheds.