Abstract:This review aims to synthesize the current knowledge of sediment dynamics using insights from long‐term research conducted in the watershed draining to the Chesapeake Bay, the largest estuary in the U.S., to inform management actions to restore the estuary and its watershed. The sediment dynamics of the Chesapeake are typical of many impaired watersheds and estuaries around the world, and this synthesis is intended to be relevant and transferable to other sediment‐impaired systems. The watershed's sediment sou… Show more
“…Our logistic regression model suggests that when using the continuous version of agriculture and when put into context with other landscape variables, the likelihood of a degraded stream condition increased 2.0% for every unit increase in agriculture in upstream watersheds. This, combined with our contingency table analysis where we found no evidence of a flow-alteration effect on stream condition in the agriculture-focused dataset, suggests that other stressors associated with agriculture (e.g., sediment (Noe et al 2020 ) and nutrients (Ator et al 2020 )) may be stronger factors affecting macroinvertebrates. Our logistic regression model also supports the importance of other variables as, in addition to the intensity of hydrologic alteration and urban development, we found several natural landscape variables (bioregion, drainage area, elevation, depth to the water table, calcium oxide lithology, % grasslands, and % wetland cover) and additional anthropogenic landscape variables (total freshwater withdrawals, % barren land cover) significant.…”
Section: Discussionsupporting
confidence: 51%
“…5 ) may be more responsive to management practices because of fewer aspects of the hydrograph requiring remediating. We acknowledge that flow is one of many possible stressors and the most effective use of our results will be when they are put into context with other leading stressors for the Chesapeake Bay watershed (e.g., sediment (Noe et al 2020 ) and nutrients (Ator et al 2020 )). Fig.…”
Regionally scaled assessments of hydrologic alteration for small streams and its effects on freshwater taxa are often inhibited by a low number of stream gages. To overcome this limitation, we paired modeled estimates of hydrologic alteration to a benthic macroinvertebrate index of biotic integrity data for 4522 stream reaches across the Chesapeake Bay watershed. Using separate random-forest models, we predicted flow status (inflated, diminished, or indeterminant) for 12 published hydrologic metrics (HMs) that characterize the main components of flow regimes. We used these models to predict each HM status for each stream reach in the watershed, and linked predictions to macroinvertebrate condition samples collected from streams with drainage areas less than 200 km2. Flow alteration was calculated as the number of HMs with inflated or diminished status and ranged from 0 (no HM inflated or diminished) to 12 (all 12 HMs inflated or diminished). When focused solely on the stream condition and flow-alteration relationship, degraded macroinvertebrate condition was, depending on the number of HMs used, 3.8–4.7 times more likely in a flow-altered site; this likelihood was over twofold higher in the urban-focused dataset (8.7–10.8), and was never significant in the agriculture-focused dataset. Logistic regression analysis using the entire dataset showed for every unit increase in flow-alteration intensity, the odds of a degraded condition increased 3.7%. Our results provide an indication of whether altered streamflow is a possible driver of degraded biological conditions, information that could help managers prioritize management actions and lead to more effective restoration efforts.
“…Our logistic regression model suggests that when using the continuous version of agriculture and when put into context with other landscape variables, the likelihood of a degraded stream condition increased 2.0% for every unit increase in agriculture in upstream watersheds. This, combined with our contingency table analysis where we found no evidence of a flow-alteration effect on stream condition in the agriculture-focused dataset, suggests that other stressors associated with agriculture (e.g., sediment (Noe et al 2020 ) and nutrients (Ator et al 2020 )) may be stronger factors affecting macroinvertebrates. Our logistic regression model also supports the importance of other variables as, in addition to the intensity of hydrologic alteration and urban development, we found several natural landscape variables (bioregion, drainage area, elevation, depth to the water table, calcium oxide lithology, % grasslands, and % wetland cover) and additional anthropogenic landscape variables (total freshwater withdrawals, % barren land cover) significant.…”
Section: Discussionsupporting
confidence: 51%
“…5 ) may be more responsive to management practices because of fewer aspects of the hydrograph requiring remediating. We acknowledge that flow is one of many possible stressors and the most effective use of our results will be when they are put into context with other leading stressors for the Chesapeake Bay watershed (e.g., sediment (Noe et al 2020 ) and nutrients (Ator et al 2020 )). Fig.…”
Regionally scaled assessments of hydrologic alteration for small streams and its effects on freshwater taxa are often inhibited by a low number of stream gages. To overcome this limitation, we paired modeled estimates of hydrologic alteration to a benthic macroinvertebrate index of biotic integrity data for 4522 stream reaches across the Chesapeake Bay watershed. Using separate random-forest models, we predicted flow status (inflated, diminished, or indeterminant) for 12 published hydrologic metrics (HMs) that characterize the main components of flow regimes. We used these models to predict each HM status for each stream reach in the watershed, and linked predictions to macroinvertebrate condition samples collected from streams with drainage areas less than 200 km2. Flow alteration was calculated as the number of HMs with inflated or diminished status and ranged from 0 (no HM inflated or diminished) to 12 (all 12 HMs inflated or diminished). When focused solely on the stream condition and flow-alteration relationship, degraded macroinvertebrate condition was, depending on the number of HMs used, 3.8–4.7 times more likely in a flow-altered site; this likelihood was over twofold higher in the urban-focused dataset (8.7–10.8), and was never significant in the agriculture-focused dataset. Logistic regression analysis using the entire dataset showed for every unit increase in flow-alteration intensity, the odds of a degraded condition increased 3.7%. Our results provide an indication of whether altered streamflow is a possible driver of degraded biological conditions, information that could help managers prioritize management actions and lead to more effective restoration efforts.
“…These restoration efforts include hundreds of Tasmanian estuaries (Coughanowr and Whitehead, 2013;Murphy et al, 2003), which suffer from centuries of human-caused degradation resulting from urbanization, introduction of invasive species, forestry, mining, fishing, agriculture, and tourism (Augustineus et al, 2010;Butler, 2006;Davis and Kidd, 2012;Ellison and Sheehan, 2014;Jones et al, 2003;Martin-Smith and Vincent, 2005;Nanson et al, 1994;Seen et al, 2004). Active conservation, restoration, and monitoring efforts are underway at many Tasmanian estuaries (Beard et al, 2008;Crawford and White, 2005;Creighton et al, 2015); none quantify geologically-relevant erosion rates nor sediment delivery, despite a recognized need to lower sediment delivery in order to reduce nutrient and pollutant loads, improve water clarity, and prevent burial of hard surfaces important for marine life (Elliott et al, 2007;Geist and Hawkins, 2016;Noe et al, 2020;Verdonschot, 2013).…”
Section: Importance Of Erosion Of George River and The Georges Bay Watershedmentioning
Abstract. Long-term erosion rates in Tasmania, at the southern end of Australia’s Great Dividing Range, are poorly known, yet such knowledge is critical for making informed land-use decisions and improving ecological health of coastal ecosystems. Here, we present the first quantitative, geologically-relevant estimates of erosion rates for the George River basin, in northeast Tasmania, based on in-situ produced 10Be (10Bei) measured from stream sand at two trunk channel sites and seven tributaries (average 10.5 mm kyr−1). These new 10Bei-based erosion rates are strongly related to mean annual precipitation rates and elevation, and we suggest that the current East-West precipitation gradient across George River greatly influences erosion in northeast Tasmania. This stands in contrast to erosion rates along the mainland portions of Australia’s Great Dividing Range, which are more strongly related to basin slope. We also extract and measure meteoric 10Be (10Bem) from sediment grain coatings of the stream sand at each site, which we use to estimate 10Bem-based erosion and denudation rates for George River. 10Bem based erosion and denudation metrics, particularly those from the central and eastern tributaries, are also closely related to elevation and precipitation in the same manner as 10Bei erosion rates. Although 10Bem-based denudation rates replicate 10Bei erosion rates within a factor of two, 10Bem-based erosion rates are systematically 5–6x higher than 10Bei erosion rates. 10Bem erosion and denudation metrics for the westernmost headwater catchments are significantly lower than expected and have likely been affected by intensive and widespread topsoil erosion related to forestry, which delivers large volumes of sediment rich in 10Bem to tributary streams. The 10Bei erosion rates presented in this study may be useful for land managers seeking to restore ecological health of Tasmania’s estuaries by reducing sediment input to levels prior to landscape disturbance.
“…Some examples include where legacy sediments have dramatically altered stream morphology and comprise large sediment storage reservoirs (Jackson et al 2005; James 2013), streams are incising due to crustal rebound after glaciation (Riedel et al 2005), or where streams are adjusting to a sudden base‐level change (Gran et al 2011). Legacy sediment deposited as a result of anthropogenic land use (such as clearcutting or grazing), and channel alterations due to historic anthropogenic activities (e.g., log drives, beaver trapping, and placer mining) will also influence the potential for indirect effects to occur (Wohl and Merritts 2007; Noe et al 2020). For example, where legacy sediments are pervasive in the mid‐Atlantic Chesapeake Bay watershed, implementation of traditional agricultural and upland BMPs is expected to decrease sediment yields eventually, but reworking of legacy sediments within the channel may confound and mask the effect of these BMPs for years to come (Noe et al 2020).…”
Section: Direct and Indirect Effectsmentioning
confidence: 99%
“…Legacy sediment deposited as a result of anthropogenic land use (such as clearcutting or grazing), and channel alterations due to historic anthropogenic activities (e.g., log drives, beaver trapping, and placer mining) will also influence the potential for indirect effects to occur (Wohl and Merritts 2007; Noe et al 2020). For example, where legacy sediments are pervasive in the mid‐Atlantic Chesapeake Bay watershed, implementation of traditional agricultural and upland BMPs is expected to decrease sediment yields eventually, but reworking of legacy sediments within the channel may confound and mask the effect of these BMPs for years to come (Noe et al 2020).…”
Managed forests generally produce high water quality, but degradation is possible via sedimentation if proper management is not implemented during forest harvesting. To mitigate harvesting effects on total watershed sediment yield, it is necessary to understand all processes that contribute to these effects. Forest harvesting best management practices (BMPs) focus almost exclusively on overland sediment sources, whereas in‐and‐near stream sources go unaddressed although they can contribute substantially to sediment yield. Thus, we propose a new framework to classify forest harvesting effects on stream sediment yield according to their direct and indirect processes. Direct effects are those caused by erosion and sediment delivery to surface water from overland sources (e.g., forest roads). Indirect effects are those caused by a shift in hydrologic processes due to tree removal that accounts for increases in subsurface and surface flows to the stream such that alterations in water quality are not predicated upon overland sediment delivery to the stream, but rather in‐stream processes. Although the direct/indirect distinction is often implicit in forest hydrology studies, we have formalized it as a conceptual model to help identify primary drivers of sediment yield after forest harvesting in different landscapes. Based on a literature review, we identify drivers of these effects in five regions of the United States, discuss current forest management BMPs, and identify research needs.
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