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Temporal and Spatial Turbidity Patterns Over 30 Years in a Managed Forest of Western Washington 1
Author(s) -
Reiter Maryanne,
Heffner John T.,
Beech Storm,
Turner Ted,
Bilby Robert E.
Publication year - 2009
Publication title -
jawra journal of the american water resources association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.957
H-Index - 105
eISSN - 1752-1688
pISSN - 1093-474X
DOI - 10.1111/j.1752-1688.2009.00323.x
Subject(s) - turbidity , environmental science , hydrology (agriculture) , watershed , surface runoff , sediment , water quality , drainage basin , streams , spatial variability , logging , turbidite , geology , geography , ecology , forestry , oceanography , paleontology , computer network , statistics , geotechnical engineering , cartography , mathematics , machine learning , computer science , biology
Forest practices have progressively changed over the last 30 years in the Pacific Northwest to address water quality concerns. There have been some assessments of these new management practices made at a site scale but very few studies have attempted to evaluate their efficacy at reducing cumulative sediment production at a watershed scale. Such an evaluation is difficult due to the spatial and temporal variability in sediment delivery and transport processes. Due to this inherent variability, detecting a response to management changes requires a long‐term data record. We utilized a water quality dataset collected over 30 years at four locations in the Deschutes River watershed (western Washington) to assess trends in turbidity and whether sediment control procedures implemented over this time period had any detectable influence. The sample sites ranged from small headwater streams (2.4 and 3.0 km 2 ) to the mainstem of the Deschutes River (150 km 2 ). Declining trends in turbidity were detected at all the permanently monitored sites. The mainstem Deschutes River site, which integrates sediment processes from the entire study watershed, showed dramatic declines in turbidity even with continued active forest management. For the small basins, logging and road construction occurred in the 1970s and 1980s and turbidity declined thereafter, achieving prelogging levels by 2000. There are no temporal trends in flow that could be responsible for the observed trends in turbidity. Our results suggest that increased attention to reducing sediment production from roads and minimizing the amount of road runoff reaching stream channels has been the primary cause of the declining turbidity levels observed in this study.