Implications For Watershed Management Research Articles

Magnitude and hotspots of soil erosion types during heavy rainstorm events on the Loess Plateau: Implications for watershed management

In the context of climate change, rainstorm events are becoming increasingly frequent. In particular, on the Loess Plateau, heavy rainstorms are the primary cause of soil erosion. This study investigated and analysed different types of soil erosion hotspots and influencing factors in small watersheds under different rainstorm events in different areas of the Loess Plateau. The results indicate that the erosion intensities of rills, gullies, landslides and collapses ranged from 13600-46244, 1982-772201, 1163-172153 t km-2 and 1867-94985 t km-2, respectively. Newly constructed terraces exhibited an erosion intensity 1.6 times greater than that of old terraces, while terraces constructed before the rainy season in the current year exhibited an erosion damage intensity 2.6 times greater than that of terraces constructed after the rainy season in the previous year. In addition, under rainstorm conditions, landslides represented the most severe type of erosion in the watersheds, with the maximum amount of erosion accounting for more than 90 % of the total erosion amount, followed by gully or collapse erosion, with the collapse of terrace risers as the main contributor. Slope cultivation land, unpaved roads, terrace risers, and valley slopes below the gully shoulder line were identified as erosion hotspot areas. Rainstorm erosion was significantly influenced by the land use type and slope, which explained 14.2 %-41.5 % and 9.7 %-15.1 %, respectively, of the total variance in erosion intensity. We suggest that soil erosion prevention and control efforts on the Loess Plateau should focus on landslides on valley slopes below gully shoulder lines, followed by gullies on unpaved roads and the collapse of terraced fields. Drainage ditches and water cellars should be constructed above the gully shoulder line and on the inside of roads and terraces, thereby reducing erosion. Our research is crucial for optimizing and adjusting watershed management measures and preventing rainstorm erosion disasters.

Exploring potential mechanisms linking urban landscapes to instream stressors and macroinvertebrates in the Southeast Piedmont: Implications for watershed management

Urbanization has greatly degraded stream health, particularly in the rapidly urbanizing southeastern United States. Recent studies identified primary instream stressors affecting biological communities along urban gradients in the Southeast Piedmont. However, a comprehensive understanding of the complex mechanisms is still lacking, which impedes effective management actions. To improve our understanding, we investigated the potential pathways by which urbanization, as represented by the landscape development intensity index (LDII), and important environmental characteristics affected instream stressors and macroinvertebrate communities using structural equation modeling (SEM) and the U.S. Geological Survey Southeast Stream Quality Assessment dataset. We investigated the direct, indirect, and total effects of LDII and environmental characteristics on instream stressors and macroinvertebrate communities as well as the interactions of instream stressors. Moreover, we explored alternative reasonable relationships between variables by using an alternative model approach. We found that LDII had moderate to strong total effects on all instream stressors and macroinvertebrates with complex impact pathways revealed in SEM models, demonstrating the dominant impact of urban landscape development on stream ecosystems in the Southeast Piedmont. Flow disturbance and pesticides were major mediators transmitting most of LDII’s effects on macroinvertebrates. Furthermore, we found potential interactions among instream stressors, which were not widely discussed in previous studies. Compared with agricultural watersheds, urban watersheds represented different land use impact mechanisms. Our findings contributed to an improved understanding of urbanization’s impact on stream ecosystems and demonstrated the usefulness of an alternative model approach that provided insights into the underlying mechanisms. In addition, we demonstrated the utility of LDII in characterizing landscape development and improving SEM models. Finally, we explored the potential of SEM in global watershed management activities by discussing the practical implications of impact pathways and the innovative use of SEM as a decision-making tool.

Multiscale ecosystem service synergies/trade-offs and their driving mechanisms in the Han River Basin, China: implications for watershed management.

The synergies and trade-offs between ecosystem services (ESs) and their driving mechanisms are hot topics in ecology and geography research. In recent years, the Han River Basin (HRB) has been continuously impacted by high-intensity urban sprawl and the Middle Route of the South-to-North Water Diversion Project, which have posed severe threats to the ecology and regional stability along the route. It is thus critical to study the ES synergies/trade-offs and their driving mechanisms. Based on the InVEST model and the value coefficient method, four vital types of ESs in the HRB, i.e., carbon sequestration (CS), food supply (FS), net primary productivity (NPP), and water yield (WY), were evaluated at town, county, and sub-watershed scales. Then, the Pearson correlation analysis was adopted to quantify the interrelationship among different ESs. Finally, the ordinary least squares (OLS) and geographical detector model (GDM) were applied to reveal the driving mechanisms of the ES synergies/trade-offs. The results showed that (1) apart from NPP, which increased at a rate of 7.54 gC·m-2·a-1 during 2000-2018, the other three types of ESs in the HRB deteriorated, with WY almost halving. (2) While CS, FS, and WY tended to exhibit high synergistic relationships, NPP showed mostly trade-off relationships, and the evaluation scale did not affect those main relationships. (3) Precipitation is the strongest driving force for the ES synergies/trade-offs in the HRB, and natural factors are generally more influential than socioeconomic factors on the ES synergies/trade-offs. This study warns of the deteriorating ecological condition of the HRB and provides empirical evidence for the synergistic enhancement of regional ESs and the optimization of ecological management policies.

Quantify soil erosion and sediment export in response to land use/cover change in the Suha watershed, northwestern highlands of Ethiopia: implications for watershed management

Soil erosion accelerated by human activities is a critical challenge affecting soil health, agricultural productivity, food security and environmental sustainability in the highlands of Ethiopia. The aim of this study was to examine the dynamics of soil loss and sediment yield potential, and identify soil erosion hotspots using RUSLE with GIS in the Suha watershed, north western highlands of Ethiopia. Digital Elevation Model, LU/LC, rainfall, soil, and conservation practice were used as input data for RUSLE model. The estimated total annual soil loss for the entire watershed increased from 1.22 million tons in 1985 to 2.43 million tons in 2019, with average annual soil loss rates of 15.2 t ha−1 yr−1 and 31.4 t ha−1 yr−1 respectively. Total sediment yield also increased from 317.52 to 630.85 thousand tons over the past 35 years. In addition, the area of soil erosion hotspots changed from 15.2% (12,708 ha) to 32% (25,660 ha) during the same periods. Sub watershed 1, 2, 15, 17, 18, and 23 are severely degraded parts of the watershed. Expansion of agriculture and bare land as the expenses of other land use types over the past 35 years could be the major causes of extensive soil erosion risk in the watershed. Besides its temporal variability, soil loss and sediment export also showed variation between land use/cover classes. The estimated results of soil loss and sediment yield as well as soil erosion hotspots revealed that the soil erosion risk is progressively increasing during the study periods. Unless action is taken and the current condition is reversed, it will critically threat the livelihoods of the community in the watershed. Generally, the results underscore urgent demand for integrated and effective watershed management strategies.

Runoff and suspended sediment yield and implications for watershed management

Runoff and suspended sediment yield and implications for watershed management

Invasive Japanese knotweed (Reynoutria japonica Houtt.) and related knotweeds as catalysts for streambank erosion

AbstractJapanese knotweed (Reynoutria japonica) and the other invasive knotweeds, collectively known as knotweed s.l., are significant invasives worldwide, especially of riparian areas. While R. japonica and other knotweed s.l. can reproduce sexually, their dispersal to and spread within new regions is often accomplished through vegetative reproduction from rhizome and stem fragments. Once established, knotweed s.l. can displace riparian plants, meaning that soil stability once provided by displaced roots is lost, carrying significant knock‐on implications for watershed management. We propose that knotweed s.l. rhizomes both displace roots and the structure they provide to soil, and also amplify bank‐erosion forces, especially during floods. Further, erosive forces create propagules, with larger flow events creating larger numbers of propagules and providing the vector for short‐ and long‐distance downstream spread within the watershed. Induced erosion is therefore the main driver of knotweed s.l. invasions along waterways. As some hydrological regimes shift towards more frequent and severe storm events in response to climate change, positive feedback loops may develop in these regions between existing knotweed s.l. populations, sudden riverbank failure, and increased flood‐related damage, with presumably significant impacts on riparian infrastructure. While the continued spread of this invasive could have significant riparian flood resiliency consequences if left unchecked, mindful action to control these plants is likely to be beneficial financially, socially, and ecologically within any invaded watershed.

Potential for Forest Restoration and Deficit Compensation in Itacaiúnas Watershed, Southeastern Brazilian Amazon

The conservation and restoration of native vegetation is vital for providing key hydrological services (i.e., maintaining high water quality, atmospheric humidity, and precipitation patterns). However, this research area lacks fine-scale studies at the watershed level to evaluate opportunities for forest restoration and deficit (the shortfall of forest required to be restored or compensated), as well as the implications for watershed management. We provide the first fine-scale estimation of forest and deficit distribution, integrating permanent preservation areas (APPs, in Portuguese) and legal reserves (RL, in Portuguese), according to Brazilian environmental law, for the 41,300 km2 Itacaiúnas watershed in the Brazilian state of Pará, which has lost 50% of its vegetation cover. Using 30 m- and 10 m-resolution imagery, a multi-temporal land use classification was performed by geographic object-based image analysis (GEOBIA). The results were combined with a set of Brazilian regulations on the conservation and restoration of APPs and RL to assess patterns of forest cover and legal compliance. We found that the total RL deficit (4383 km2) was higher than the total forest surplus (above legal obligation) (3241 km2). However, most of this deficit (56%) could be compensated by protecting a forest area in another property within the Amazon biome, while 44% must be legally restored. Only 4% of the total forest surplus can be legally deforested, and the remaining 96% is already protected by law but can be used to compensate for areas under the deficit. We also found that, despite 57% (3017 km2) of the total APP being forested, only 26% (1356 km2) of the APP must be restored and 17% (881 km2) can remain deforested (consolidated areas). The 2012 law revision reduced the obligation to restore RL and APPs. This change could affect hydrological and ecological services. Compensation mechanisms could be used to protect forest within the Itacaiúnas watershed, rather than in the biome, to reduce further deforestation pressure.

Spatial variation in drainage characteristics and geomorphic instantaneous unit hydrograph (GIUH); implications for watershed management—A case study of the Varada River basin, Northern Karnataka

Abstract Geomorphological characteristics can be treated as signatures of hydrological responses. Geomorphologic instantaneous unit hydrograph (GIUH) is of utmost use in planning watershed management programs on a broad scale in absence of hydrologic data. Fifth order basins from different agroclimatic zones in the Varada River basin were selected to understand the spatial variation in drainage characteristics. These sub-basins show significant differences in their morphometric properties such as basin area, drainage density, bifurcation ratio, circularity ratio, constant of channel maintenance etc. These differences reflect variation in the hydrological process and geomorphologic instantaneous unit hydrograph (GIUH) of different sub-basins and can be used to understand watershed management aspects. Fifth order sub-basin in the Southern Transition agroclimatic zone is potential for artificial recharge programs. Sub-basins in the Hilly non-forest zone on the north are ideal for surface water storage like tank development program while Forested Hilly zone on the north are environmentally sensitive and prone to erosion.

Soil and nutrient retention in winter-flooded ricefields with implications for watershed management

The ability of water resources to support aquatic life and human needs depends, in part, on reducing nonpoint source pollution amid contemporary agricultural practices. Winter retention of shallow water on rice and other agricultural fields is an accepted management practice for wildlife conservation; however, soil and water conservation benefits are not well documented. We evaluated the ability of four post-harvest ricefield treatment combinations (stubble-flooded, stubble-open, disked-flooded and disked-open) to abate nonpoint source exports into watersheds of the Mississippi Alluvial Valley. Total suspended solid exports were 1,121 kg ha-1 (1,000 lb ac-1) from disked-open fields where rice stubble was disked after harvest and fields were allowed to drain, compared with 35 kg ha-1 (31 lb ac-1) from stubble-flooded fields where stubble was left standing after harvest and fields captured rainfall from November 1 to March 1. Estimates of total suspended solid exports from ricefields based on Landsat imagery and USDA crop data are 0.43 and 0.40 Mg km-2 day-1 in the Big Sunflower and L'Anguille watersheds, respectively. Estimated reductions in total suspended solid exports from ricefields into the Big Sunflower and L'Anguille watersheds range from 26% to 64% under hypothetical scenarios in which 65% to 100% of the rice production area is managed to capture winter rainfall. Winter ricefield management reduced nonpoint source export by decreasing concentrations of solids and nutrients in, and reducing runoff volume from, ricefields in the Mississippi Alluvial Valley.

Effects of PVC, cast iron and concrete conduit on concentrations of copper in stormwater

Architectural applications of copper on roofs, gutters and facades exposes it to weathering forces, such as wind and all forms of precipitation. This leads to the dissolution of copper from these surfaces and its introduction into local watersheds. The potential for exposure in local watersheds is a function of the amount of copper entering the watershed and the assimilation capacity of a wide variety of natural and manmade substrates that transform and sequester copper, thus reducing exposure of sensitive organisms to bioavailable copper. This study investigates one type of manmade substrate, stormwater conduit, commonly used to transport stormwater away from buildings. Conduits made of PVC and cast iron did not significantly remove copper from a synthetic stormwater spiked with copper averaging 2391 μg Cu/L. Concrete conduit significantly removed copper from the synthetic water and at high rates (12 – 18%) over a short distance (610 cm). A high percentage (81 – 100%) of the copper removed from the water was from the dissolved copper fraction. Once adsorbed to the concrete, copper did not readily leach back into copper-free water subsequently pumped into the conduit. These characteristics have significant implications for watershed management and best management practices for reducing concentrations of copper in stormwater runoff.

Estimating accumulation rates and physical properties of sediment behind a dam: Englebright Lake, Yuba River, northern California

Studies of reservoir sedimentation are vital to understanding scientific and management issues related to watershed sediment budgets, depositional processes, reservoir operations, and dam decommissioning. Here we quantify the mass, organic content, and grain‐size distribution of a reservoir deposit in northern California by two methods of extrapolating measurements of sediment physical properties from cores to the entire volume of impounded material. Englebright Dam, completed in 1940, is located on the Yuba River in the Sierra Nevada foothills. A research program is underway to assess the feasibility of introducing wild anadromous fish species to the river upstream of the dam. Possible management scenarios include removing or lowering the dam, which could cause downstream transport of stored sediment. In 2001 the volume of sediments deposited behind Englebright Dam occupied 25.5% of the original reservoir capacity. The physical properties of this deposit were calculated using data from a coring campaign that sampled the entire reservoir sediment thickness (6–32 m) at six locations in the downstream ∼3/4 of the reservoir. As a result, the sediment in the downstream part of the reservoir is well characterized, but in the coarse, upstream part of the reservoir, only surficial sediments were sampled, so calculations there are more uncertain. Extrapolation from one‐dimensional vertical sections of sediment sampled in cores to entire three‐dimensional volumes of the reservoir deposit is accomplished via two methods, using assumptions of variable and constant layer thickness. Overall, the two extrapolation methods yield nearly identical estimates of the mass of the reservoir deposit of ∼26 × 106 metric tons (t) of material, of which 64.7–68.5% is sand and gravel. Over the 61 year reservoir history this corresponds to a maximum basin‐wide sediment yield of ∼340 t/km2/yr, assuming no contribution from upstream parts of the watershed impounded by other dams. The uncertainties and limitations of the estimates of overall sediment quantities are discussed. Implications for watershed management and future reservoir sedimentation studies are also presented.

Rainwater management for increased productivity among small-holder farmers in drought prone environments

A critical analysis of conventional water resources assessments and re-visiting the on-farm water balance suggests large scopes for water productivity improvements in small-holder rainfed farming systems in drought prone environments of Eastern and Southern Africa. The paper addresses key management challenges in trying to upgrade rainfed agriculture, and presents a set of field experiences on system options for increased water productivity in small-holder farming. Implications for watershed management are discussed, and the links between water productivity for food and securing of water flow to sustain ecosystem services are briefly analysed. Focus is on sub-Saharan Africa hosting the largest food deficit and water scarcity challenges.The paper shows that there are no agro-hydrological limitations to doubling on-farm staple food yields even in drought prone environments, by producing more “crop per drop” of rain. Field evidence is presented suggesting that meteorological dry spells are an important cause for low yield levels and it is hypothesised that this may constitute a core driver behind farmers risk aversion strategies. The dry spell induced risk perceptions contribute amongst others to soil nutrient mining due to insignificant investments in fertilisation. For many small-holder farmers in the semi-arid tropics it is simply not worth investing in fertilisation (and other external inputs) as long as the risk for crop failure remains a reality every fifth year with risk of yield reductions every second year, due to periodic water scarcity during the growing season (i.e., not necessarily cumulative water scarcity).Results are presented from field research on small-holder system innovations in the field of water harvesting and conservation tillage. Upgrading rainfed production systems through supplemental irrigation during short dry-spells is shown to dramatically increase water productivity. Downstream implications of increased upstream withdrawals of water for upgrading of rainfed food production are discussed.Finally it is argued that some of the most exciting opportunities for water productivity enhancements in rainfed agriculture are found in the realm of integrating components of irrigation management within the context of rainfed farming, e.g., supplemental or micro irrigation for dry spell mitigation. Combining such practices with management strategies that enhance soil infiltration, improve water holding capacity and plant water uptake potential, can have strong impact on agricultural water productivity. This suggests that it is probably time to abandon the largely obsolete distinction between irrigated and rainfed agriculture, and instead focus on integrated rainwater management.