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The Regulation and Management of Bottomland Hardwood Forest Wetlands: Implications of the EPA-Sponsored Workshops
Published in James G. Gosselink, Lyndon C. Lee, Thomas A. Muir, Ecological Processes and Cumulative Impacts, 2020
James G. Gosselink, Lyndon C. Lee, Thomas A. Muir
Inability of the §404 program to manage cumulative impacts is compounded by the issuance of nationwide permits, particularly Nationwide Permit 26 (33 CFR 330.5 (a)(26)). This general permit, which allows up to 10 acres of fill to be placed into headwater wetlands (wetlands located in headwater reaches of tributary streams with a mean annual flow of less than 5 ft3 sec−1) and in isolated wetlands (wetlands that are not bordering, neighboring, or contiguous to Waters of the United States), effectively exempts about 7 million ha of wetlands from regulation (Anonymous 1988), and may have led to significant cumulative impacts to water quality, hydrology, and food web support functions throughout the range of forested wetlands in the Southeastern and Mid-Atlantic states. Headwaters are critically important because they form the primary contact between terrestrial and aquatic ecosystems in landscapes that support bottomland hardwood wetlands. They also exist as the headward-most member of bottomland hardwood wetland continua.
Hydrological modelling of the Kaap catchment
Published in Aline Maraci Lopes, Saraiva Okello, Improved Hydrological Understanding of a Semi-Arid Subtropical Transboundary Basin Using Multiple Techniques – The Incomati River Basin, 2019
Aline Maraci Lopes, Saraiva Okello
Another issue of uncertainty is the configuration of the groundwater reservoirs. From the shape of the observed hydrograph it appears that the recession is not linear, but rather logarithmic or another non-linear function. The research using tracers (Camacho Suarez et al., 2015) revealed that there are two distinct groundwater components in the Kaap outlet, which can be indicative of different reservoirs that operate with distinct dynamics. Shallow groundwater responds quickly in rainfall events, and has the highest contribution to flow, particularly when the antecedent moisture in the catchment is already high. The other groundwater component is from deeper sources, which could be the regional groundwater, recharged in the headwaters of the catchment. This component is responsible for sustaining the baseflow during most of the year. In the months of February to April, when the catchments are already quite wet, most of the runoff is generated through direct runoff (Chapter 5).
Introduction to Hydrological Problems and Environmental Management in Highlands and Headwaters
Published in Josef Křeček, G.S. Rajwar, Martin J. Haigh, Hydrological Problems and Environmental Management in Highlands and Headwaters, 2017
Martin J. Haigh, Josef Křeček, G.S. Rajwar
Highland and headwater regions, then, lie on the front lines of economic exploitation for many nations. They also tend to lie on the front-lines of political and cultural conflict. Since, by definition, highlands and headwaters are the source regions for a nation’s water resources and since, normally, these marginal areas are the places where national boundaries meet, and sometimes overlap, highlands and headwaters have a significance which is far greater than either their internal resource potential or relatively small populations might warrant. Adverse changes in these areas can have very dramatic effects on both the environmental and political stability of a nation. Hydrological problems in the headwaters can change the patterns of flooding, sedimentation and river flow in areas hundreds of kilometres downstream. Problems of unrest on a nation’s borders can send shock waves that rock governments thousands of kilometres away in the nation’s capital.
Impacts of damming and climate change on the ecosystem structure of headwater streams: a case study from the Pyrenees
Published in Inland Waters, 2022
Alejandro López-de Sancha, Romero Roig, Iara Jiménez, Anna Vila-Gispert, Helena Guasch
Conservation of headwater streams is a fundamental consideration that must be addressed to effectively preserve freshwater ecosystems (Biggs et al. 2017). Because up to 90% of a river’s flow is derived from headwater streams (Saunders et al. 2009), they play a vital role in whole river basins and are fundamental for the correct maintenance of the ecological integrity of a river network. In a climate change context, these ecosystems play a key role in river basins by providing water, ameliorating floods, transferring nutrients and carbon, intercepting pollutants, and supplying sediments (Biggs et al. 2017). Considering that the presence of dams is common in headwater streams from many mountain ranges and that climate change will decrease the water availability in these ecosystems, the maintenance and restoration of a sufficient ecological flow in dam-impounded streams should be promoted (Rudra 2018). More research is needed on the resistance and resilience of small headwater stream ecosystems to anthropogenic disturbances (Biggs et al. 2017), and our results highlight the importance of field studies in the assessment of how multiple anthropogenic stressors interact in an applied context.
Hydraulic drivers of populations, communities and ecosystem processes
Published in Journal of Ecohydraulics, 2021
Aaron I. Packman, Christopher T. Robinson, Nicolas Lamouroux
Beyond the well-established effects of dams fragmenting river ecosystems, increased damming of headwaters and large-scale water diversions affect downstream river ecosystems by dewatering rivers, shifting patterns of sediment deposition and aggradation, and reducing habitat heterogeneity (Veldkamp et al. 2017; Sabater et al. 2018; Best 2019). Ongoing land development and industrial agricultural practices are also accelerating soil erosion and export of nutrients from the terrestrial landscape to the aquatic environment (Blann et al. 2009; Seitzinger et al. 2010; Borrelli et al. 2017). Globally, the cumulative effects of these changes are altering continental balances of water (increasing evaporation from the continents to the atmosphere) (Jaramillo and Destouni 2015; Rodell et al. 2018; Zhan et al. 2019), eroding and exporting large amounts of soils and sediments (Borrelli et al. 2017; Best 2019), and greatly increasing the delivery of nutrients from the continents to the oceans (Seitzinger et al. 2010; Beusen et al. 2016; Sinha et al. 2017). Increased information on links between watershed management, river flow, river hydraulics and habitats, and ecosystems is needed to ensure the sustainability of water resources and maintain the integrity of aquatic ecosystems.
Dynamics of heavy metals in the fine sediments from a subtropical forest headwater stream during a rainy season
Published in Inland Waters, 2023
Zemin Zhao, Fuzhong Wu, Yan Peng, Petr Heděnec, Yuan Wang, Wanrong Hu, Xiangyin Ni, Kai Yue
Headwater streams emerge from ravines and are commonly <1.3 m wide and 500 m long, driving the sources of the downstream connected rivers (Freeman et al. 2007). The length of headwater streams makes up a significant portion of the river network, often as much as 85% (Downing et al. 2012). Headwater streams link uplands to rivers and represent a key connection in the dynamic transformation of organic matter and the energy source–sink relationship between terrestrial and aquatic ecosystems (Li et al. 2021, Rosentreter et al. 2021). The preponderance and position of headwater streams as riverine capillaries may substantially control the functional integrity of the entire river network. Every major feature of the river geomorphic system, the river chemical system, and the river ecosystem begins in headwater streams (Freeman et al. 2007). Sediment is an important component of headwater stream ecosystems (Majdi et al. 2017), especially fine sediments (defined here as <2 mm in diameter), which are highly mobile once they enter the stream (Phillips et al. 2021). As one of the primary carriers of transported stream material, sediment has a significant effect on material export from headwater streams, driving the cycling, transport, and storage of elements in streams (Wilkes et al. 2019). Indeed, fine sediments usually have higher organic matter concentration than that of coarse sediments (Mondon et al. 2021) but also are the primary reservoir of heavy metals in stream ecosystems (Banerjee et al. 2016, Li et al. 2019). Thus, their dynamics are important in the total storge of heavy metals in the whole sediment composition. As illustrated by previous research (Zheng et al. 2008, Wang et al. 2011), 30–98% of heavy metals in rivers were transported as sediment-associated forms, whereas >90% of the heavy metal loads in stream ecosystems were associated with suspended fine matter and sediments. Once they reach critical concentrations, river heavy metals trend toward toxicity (Niu et al. 2021), especially lead (Pb) and cadmium (Cd), which are extremely toxic regardless of their trace levels (Ali et al. 2020); therefore, heavy metal dynamics in river and estuary sediments are an increasing environmental concern (Xiao et al. 2021). Despite much research on loading and distribution of heavy metals in rivers and estuaries in recent decades, few investigations have addressed heavy metals in headwater stream sediments, thus limiting our understanding of heavy metal dynamics under natural conditions.