Land use and wetland drainage affect water levels and dynamics of remaining wetlands

Abstract

Abstract. Depressional wetlands are productive and unique ecosystems found around the world. Their value is due, in part, to their dynamic nature, in which water levels fluctuate in response to climate, occasionally drying out. However, many wetlands have been altered by consolidation drainage, where multiple, smaller wetlands are drained into fewer, larger, wetlands causing higher water levels. We evaluated whether current (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) water surface areas were greater than historical water surface areas of 141 randomly selected semipermanent and permanent wetlands across the Prairie Pothole Region of North Dakota, USA. We also evaluated whether differences between historical and current hydrology of these wetlands were attributable to consolidation drainage. For each of these wetlands, we digitized water surface areas from aerial photography during historical and current eras. Our results indicated that water surface areas are currently 86% greater in sample wetlands than they were historically and that differences can be attributed to consolidation drainage. Water surface areas of consolidated wetlands in extensively drained landscapes were 197% greater than those with no drainage and now require more extreme drought conditions to dry out. Wetlands in extensively drained catchments were larger, dry out less frequently, and have more surface-water connections to other wetlands via ditches. These factors make conditions more favorable for the presence of fish that decrease abundances of aquatic invertebrates and reduce the productivity and quality of these wetlands for many species. Our results support the idea that intact wetlands serve an important role in water storage and groundwater recharge and reduce down-stream runoff.

The Challenges of Remote Monitoring of Wetlands

“…Land use and management actions already have been responsible for substantial losses and alterations of wetlands [55,56], and anthropogenic activities continue to alter the surface of the Earth across large geographic extents at rapid rates (e.g., [57]). Presence of water and quality of habitat in wetlands can be manipulated through direct actions (e.g., [58]), but wetlands also are heavily influenced by many biotic and abiotic exogenous factors, and drivers of change, especially socioeconomic drivers, may be geographically removed from wetlands (e.g., [59,60]). As the human population continues to increase across the planet, so do concomitant increases in demands for ecosystem services [61].…”

Patterns and drivers for wetland connections in the Prairie Pothole Region, United States

“…In ecoregions with low drainage development, surface water is being stored in glacially formed depressions (Winter and Rosenberry 1998;Stokes et al 2007), resulting in an inverse relationship between stream density and surface-water extent (Table 10). The drainage network in the PPR is also increasingly modified with the expansion of ditch networks and tile drainage in association with agricultural activities (McCauley et al 2015). Ditches, pipes and field tiles can increase connectivity between waterbody features, however, both filling wetlands with soil and lowering the water table through increased water withdrawal can decrease expected surface-water connectivity (DeLaney 1995;Blann et al 2009;McCauley et al 2015).…”

“…The drainage network in the PPR is also increasingly modified with the expansion of ditch networks and tile drainage in association with agricultural activities (McCauley et al 2015). Ditches, pipes and field tiles can increase connectivity between waterbody features, however, both filling wetlands with soil and lowering the water table through increased water withdrawal can decrease expected surface-water connectivity (DeLaney 1995;Blann et al 2009;McCauley et al 2015). Our finding regarding the importance of predicted anthropogenic drainage may be related to the relation between land use and wetland connectivity and wetland loss (Miller et al 2009;Van Meter and Basu 2015).…”

“…As depressional wetlands are typically non-channel connected (Tiner 2003), surface-water connections with other water bodies are usually not continuous. Under wet conditions, however, many of these wetlands cyclically or episodically exchange or contribute water to other wetlands, open waters, and/or streams through temporary overland or shallow groundwater flows, unmapped ditches or channels, and/or the merging of wetland waters in low relief areas (Rains et al 2006(Rains et al , 2008Cook and Hauer 2007;Sass and Creed 2008;Kahara et al 2009;Wilcox et al 2011;McCauley et al 2015). During flood events or wet periods, depressional wetlands that become connected to streams or subsumed by lakes exchange water and materials, but may experience the temporary loss of wetland function until water levels recede (Junk et al 1989;Galat et al 1998;Mortsch 1998).…”

“…However, most of these efforts have been theoretical and have not related dynamic spatial variables, such as distance, to changes in actual surface-water extent. In addition to landscape position, the probability of connectivity for an individual wetland can also be expected to depend on climate, which influences the magnitude, frequency and duration of water inputs (Phillips et al 2011); topography, which influences the capacity for surface-water expansion (Rover et al 2011;Shaw et al 2013); and anthropogenic drainage (i.e., ditches and tile drainage), which modifies topographical flows of surface water (McCauley et al 2015). Although existing research has contributed to our ability to predict fill-and-spill on the scale of individual wetlands (Huang et al 2011b) and in small, heavily instrumented watersheds (Shaw et al 2012;Spence and Phillips 2014), efforts to understand the abundance of surface-water connections on a landscape scale have been minimal.…”