Hot spots and hot moments in riparian zones: potential for improved water quality management

Authors: VIDON, PHILIPPE - Indiana University; ALLAN, CRAIG - University Of North Carolina; BURNS, DANIEL - Us Geological Survey (USGS); DUVAL, THOMAS - McMaster University; GURWICK, NOEL - Carnegie Institute - Stanford; INAMDAR, SHREERAM - University Of Delaware; Lowrance, Robert; OKAY, JUDY - Chesapeake Bay Foundation; SCOTT, DURWOOD - Virginia Polytechnic Institution & State University; SEBESTYEN, SCOTT - US Department Of Agriculture (USDA)

Submitted to: Journal of American Water Works Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2009
Publication Date: 8/1/2010
Citation: Vidon, P., Allan, C., Burns, D., Duval, T., Gurwick, N., Inamdar, S., Lowrance, R.R., Okay, J., Scott, D., Sebestyen, S. 2010. Hot spots and hot moments in riparian zones: potential for improved water quality management. Journal of American Water Works Association. 46(2):278-298.

Interpretive Summary: Despite considerable variation over both space and time, biological, chemical, geological (the combination of which is called biogeochemical) and hydrological processes in riparian (streamside) zones regulate are known to help control the movement of nonpoint source pollution and other contaminants. Recently, these heterogeneous processes have been conceptualized as “hot spots” and “hot moments”, the discrete places and times that have disproportionate effects at the landscape scale. Thus far, studies investigating the importance of hot phenomena (spots and moments) in riparian zones have largely focused on nitrogen (N) despite compelling evidence that hot spots and moments have important controls on a variety of elements, chemicals, and particulate contaminants. In addition to N, this review summarizes current knowledge for phosphorus (P), organic matter (OM), pesticides, and mercury (Hg) across the upland/riparian/stream interface, identifies variables controlling the occurrence and magnitude of hot phenomena in riparian zones for these contaminants, and discusses the implications for riparian zone management of recognizing the importance of hot phenomena in understanding the transport of pollutants at the watershed scale. Examples are presented to show that biogeochemical process-driven hot spots and moments occur along the stream/riparian zone/upland interface for a wide variety of pollutants. In most cases, hot spots or hot moments of retention, degradation, or production occur because of unique combinations of soil properties and hydrological conditions. However, high net contaminant processing is only maximized when biogeochemical hot spots are co-located with high rates of contaminant input. A basic understanding of the possible co-occurrence, if any, of hot spots and moments for a variety of contaminants in riparian systems will increase our understanding of the influence of riparian zones on water quality. This critical information is needed to better understand how stream and riparian zone management affect pollutant generation and removal.

Technical Abstract: Despite considerable heterogeneity over space and time, biogeochemical and hydrological processes in riparian zones regulate contaminant movement to receiving waters and often mitigate the impact of upland sources of contaminants on water quality. Recently, these heterogeneous processes have been conceptualized as “hot spots” and “hot moments”, the discrete places and times that have disproportionate effects at the landscape scale. Thus far, studies investigating the importance of hot phenomena (spots and moments) in riparian zones have largely focused on nitrogen (N) despite compelling evidence that hot spots and moments have important controls on a variety of elements, chemicals, and particulate contaminants. In addition to N, this review summarizes current knowledge for phosphorus (P), organic matter (OM), pesticides, and mercury (Hg) across the upland/riparian/stream continuum, identifies variables controlling the occurrence and magnitude of hot phenomena in riparian zones for these contaminants, and discusses the implications for riparian zone management of recognizing the importance of hot phenomena in annual solute budgets at the watershed scale. Examples are presented to show that biogeochemical process-driven hot spots and moments occur along the stream/riparian zone/upland interface for a wide variety of constituents. In most cases, hot spots or hot moments of retention, degradation, or production occur because of unique combinations of electron donors and acceptors, oxidation-reduction (redox) conditions, and hydrological conditions. However, high net contaminant processing is only maximized when biogeochemical hot spots are synchronous with transport driven hot spots and moments. A basic understanding of the possible co-occurrence, if any, of hot spots and moments for a variety of contaminants in riparian systems will increase our understanding of the influence of riparian zones on water quality. This critical information is needed to better understand how stream and riparian zone management affect pollutant generation and removal.