Natural and Post-Urbanization Signatures of Hypoxia in Two Basins of Puget Sound: Historical Reconstruction of Redox Sensitive Metals and Organic Matter Inputs

Abstract

Hypoxia has been observed in Hood Canal, Puget Sound, WA, USA since the 1970s. Four long sediment cores were collected in 2005 and age-dated to resolve natural and post-urbanization signatures of hypoxia and organic matter (OM) sources in two contrasting basins of Puget Sound: Main Basin and Hood Canal. Paleoecological indicators used for sediment reconstructions included pollen, stable carbon and nitrogen isotopes (d 13 C and d 15 N), biomarkers of terrestrial OM (TOM), biogenic silica (BSi), and redoxsensitive metals (RSM). The sedimentary reconstructions illustrated a gradient in RSM enrichment factors as Hood Canal [ Main Basin, southern [ northern cores, and pre1900s [ 1900-2005. The urbanization of Puget Sound watersheds during the 1900s was reflected as shifts in all the paleoecological signatures. Pollen distributions shifted from predominantly old growth conifer to successional alder, dominant OM signatures recorded a decrease in the proportion of marine OM (MOM) concomitant with an increase in the proportion of TOM, and the weight % of BSi decreased. However, these shifts were not coincidental with an overall increase in the enrichment of RSM or d 15 N signatures indicative of cultural eutrophication. The increased percentage of TOM was independently verified by both the elemental ratios and lignin yields. In addition, isotopic signatures, BSi, and RSMs all suggest that OM shifts may be due to a reduction in primary productivity rather than an increase in OM regeneration in the water column or at the sediment/water interface. Therefore, the reconstructions suggested the Hood Canal has been under a more Electronic supplementary material The online version of this article (oxygenated ''stance'' during the twentieth century compared to prior periods. However, these 2005 cores and their resolutions do not encompass the period of high resolution water column measurements that showed short-lived hypoxia events and fish kills in Hood Canal during the early twenty-first century. The decoupling between the increased watershedscale anthropogenic alterations recorded in the OM signatures and the relatively depleted RSM during the twentieth century suggests that physical processes, such as deep-water ventilation, may be responsible for the historical variation in oxygen levels. Specifically, climate oscillations may influence the ventilation and/or productivity of deep water in Puget Sound and particularly their least mixed regions.

Seasonal Carbonate Chemistry Covariation with Temperature, Oxygen, and Salinity in a Fjord Estuary: Implications for the Design of Ocean Acidification Experiments

“…Due to sluggish circulation and the availability of nutrients in inflowing marine and terrestrial waters, hypoxic conditions commonly occur in Hood Canal during the summer months [49]. As evidenced by oxygen and pCO 2 depth profiles in August 2008 and September 2009, aerobic respiration simultaneously draws down O 2 at depth and increases pCO 2 .…”

Species Composition and Distribution of Jellyfish in a Seasonally Hypoxic Estuary, Hood Canal, Washington

“…This contrast from expected daytime distributions is perplexing as it suggests the zooplankton sensed and avoided hypoxia, but in October, they were most abundant in the near-surface hypoxic layer where oxygen was 1.5-1.8 mg L −1 . Some reports of geographic differences in copepod response imply that only populations that inhabit historically hypoxic regions will move to avoid hypoxia [50], but Hood Canal has been hypoxic for hundreds of years [51]. There are wide differences in behavioral response to hypoxia among species in Hood Canal [52], consequently more specific taxonomic information could help explain patterns observed in this study.…”

Evaluating Effects of Stressors from Marine and Hydrokinetic Energy

“…Table 1. Estimates of water volumes, water residence times, sedimentation rates, and sediment area for the Admiralty Inlet case study (Lavelle et al 1985;Babson et al 2006;Pelletier and Mohamedali 2009;Brandenberger et al 2011). The turbine and cowling surface area of the two OpenHydro devices that will be coated with antifouling material will be on the order of 450 m 2 .…”