Hydrologic connectivity and implications for ecosystem processes - Lessons from naked watersheds

Abstract

Hydrologic connectivity has received great attention recently as our conceptual models of watersheds and water quality have evolved in the past several decades. However, the structural complexity of most temperate watersheds (i.e. connections among shallow soils, deep aquifers, the atmosphere and streams) and the dynamic seasonal changes that occur within them (i.e., plant senescence which impacts evapotranspiration) create significant challenges to characterizing or quantifying hydrologic connectivity. The McMurdo Dry Valleys, a polar desert in Antarctica, provide a unique opportunity to study hydrologic connectivity because there is no vegetative cover (and therefore no transpiration), and no deep aquifers connected to surface soils or streams. Glacier melt provides stream flow to well-established channels and closed-basin, ice-covered lakes on the valley floor. Streams are also connected to shallow hyporheic zones along their lengths, which are bounded at ~75 cm depth by ice-cemented permafrost. These hydrologic features and connections provide water for and underpin biological communities. Hence, exchange of water among them provides a vector for exchange of energy and dissolved solutes. Connectivity is dynamic on timescales of a day to a flow season (6-12 weeks), as streamflow varies over these timescales. The timescales over which the these connections occur is also dynamic. Exchanges between streams and hyporheic zones, for example, have been estimated to be as short as hours to as long as several weeks. These exchanges have significant implications for the biogeochemistry of these systems and the biotic communities in each feature. Here we evaluate the lessons we can learn about hydrologic connectivity in the MDV watersheds that are simplified in the context of processes occurring and water reservoirs included in the landscape, yet are sensitive to climate controls and contain substantial physical

Linking hydrologic signatures to hydrologic processes: A review

“…In glacial environments where runoff is driven by meltwater and is less sensitive to precipitation variability, the year‐to‐year variability in flow magnitude and flow duration curve provide signatures for the magnitude and distribution of connection between meltwater sources and channels (Gooseff, Wlostowski, McKnight, & Jaros, ). Connectivity distribution can be quantified using a connectivity duration curve, the equivalent of the FDC (Jencso et al, ).…”

Seasonal Water Exchanges between China’s Poyang Lake and Its Saucer-Shaped Depressions on River Deltas

“…Therefore, hydrological connectivity and water exchange are especially important considerations for shallow lake-wetlands [14,15]. A better understanding of these hydrologic processes is critical to helping regulate wetland structure and assess the status of vulnerable delta systems [1,16,17].…”

“…Water 2017, 9, 884 2 of 11 understanding of these hydrologic processes is critical to helping regulate wetland structure and assess the status of vulnerable delta systems [1,16,17]. Poyang Lake is the largest shallow freshwater lake in China.…”

Trickle or treat: The dynamics of nutrient export from polar glaciers

“…Although DOC concentrations did not correlate with discharge rate, high variability in DOC concentrations may indicate that DOC is also exported downstream as episodic treats, but that the timing of these treats may not coincide with peak discharge conditions as consistently as is the case for DIN. These nutrient‐specific dynamics are not always consistent between proglacial streams in watersheds with similar climates, geology, and/or glacial thermal regimes, highlighting the important influence of dynamic changes in the connectivity of glacier‐proglacial biogeochemical systems on nutrient fluxes (Gooseff et al, ) and emphasizes the need to develop conceptual models that thoroughly describe the biogeochemical and hydrological components of the systems.…”