2008 Progress Report: Nonlinear Response of Pacific Northwest Estuaries to Changing Hydroclimatic Conditions: Flood Frequency, Recovery Time and Resilience

EPA Grant Number: R833015
Title: Nonlinear Response of Pacific Northwest Estuaries to Changing Hydroclimatic Conditions: Flood Frequency, Recovery Time and Resilience
Investigators: D'Andrea, Anthony F. , Wheatcroft, Robert A.
Current Investigators: Wheatcroft, Robert A. , D'Andrea, Anthony F.
Institution: Oregon State University
EPA Project Officer: Hiscock, Michael
Project Period: July 1, 2006 through June 30, 2010
Project Period Covered by this Report: August 1, 2007 through July 31,2008
Project Amount: $620,182
RFA: Nonlinear Responses to Global Change in Linked Aquatic and Terrestrial Ecosystems and Effects of Multiple Factors on Terrestrial Ecosystems: A Joint Research Solicitation- EPA, DOE (2005) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Ecosystems , Climate Change


Rainfall intensity is on the rise and the sediment yield from Pacific Northwest (PNW) basins has increased. Consequently, sediment input to estuaries has increased in magnitude and intensity, with important, but unknown ramifications for the health of, and ecosystem services provided by, PNW estuaries. However, it is difficult to evaluate the risk to estuarine ecosystems because the studies to date have tracked only a handful of species and rarely track recovery from the flood sedimentation events. Without a community‐level understanding of the changes in biodiversity and functional redundancy in the intertidal benthic ecosystem, it is difficult to assess the risk of flood sedimentation to Pacific estuaries. The questions that motivate the research are (1) What is the impact of flood events on the mortality, functional group composition, and resilience of the intertidal macrobenthic invertebrate community?; (2) How does the within‐year frequency of flood events affect the recovery of the benthic community?; and (3) Do flood sedimentation events increase the susceptibility of the benthic community to colonization by non‐indigenous species (NIS)? Hypotheses based on these research questions are being tested using a manipulative field study in Netarts Bay, Oregon.
There are four major research objectives for the project:
1) Design and implement a manipulative field study which simulates different frequencies of flood sedimentation events (no, one, or two events in a single rain season) to determine the ecological effects of flood sedimentation on intertidal benthic macroinvertebrate communities
2) Use a combination of high resolution benthic sampling and multivariate analyses of benthic community metrics to track the initial mortality, recovery, and resilience of the benthic community.
3) Collect and analyze sediment samples parallel to the benthic community samples to track changes in important sediment properties that have direct or indirect effects on survival or habitat suitability of sediments to the benthic invertebrate community.
4) Synthesize the datasets from this study to develop an empirical and theoretical framework for predicting the effects of flood sedimentation events on tideflat macrobenthic communities in PNW estuaries and how these changes impact ecologically and economically important biotic resources and ecosystem services.

Progress Summary:

Objective 1: Design and implement field study simulating flood sedimentation effects
Our progress to complete Objective 1 during the first year involved three major steps: preliminary surveys to identify sites, pilot studies to guide sampling approaches, and initiation of the full flood study. Preliminary surveys of potential study areas were conducted within the first month (August 2007) of the study. The ultimate siting of our study area was based on a combination of environmental criteria (e.g., tide height, grain size, etc.) and logistical criteria (e.g., avoiding conflict with other users, minimize disturbance). After consultation with local stakeholders and state resource agency representatives, we found a site which did not conflict with recreational or commercial uses of the intertidal while still matching the environmental criteria we had developed. The study area is 130m long by 50m wide. This study area is subdivided into 12 subunits of approximately equal size to maximize the spatial distribution of our study plots while permitting randomization of both experimental treatment and plot location. During the preliminary studies, we also identified the location of all study plots (3 replicates each of pilot study (see below), control, and one or two flood experimental treatments) using a hierarchal, stratified randomization approach.
During the first three months, we also conducted two pilot studies to test and improve the sampling and experimental approaches used in the full flood studies. The first study was conducted at the end of the initial surveys and involved randomized sampling of benthic infaunal cores within the replicate pilot study plots we established. We oversampled these plots in order to establish the appropriate diameter and number of macrofauna cores to use in the full flood experiments that maximizes statistical power while minimizing analytical costs. These samples also permitted an initial survey of the macrofaunal community and taxonomic identification of species found in the study area (Objective 2 below). The second pilot study tested our flood sedimentation simulation techniques for the full experiment. This test involved the collection of watershed terrestrial sediments, mixing sediment seawater slurries, and testing field approaches for creating the flood sedimentation layers in Netarts Bay. The results of this small‐scale test permitted us to work out the details of the larger‐scale experiment, refine our approach, and provide a more realistic estimate of manpower and time needs for the full experiment.
The initiation of the full flood experiment was conducted in January of 2008. This start date was one month later than initially planned, but our original December 2007 start was delayed due to a historic winter storm that hit the Oregon and Washington coasts in early December. The full flood study was initiated using the nine randomized, replicate plots for the control and two flood treatments set up during the preliminary survey. We initially sampled all nine plots 2 days before we simulated the first simulated flood sedimentation event on both of the sets of flood treatment plots. We initially used a high frequency sampling approach after the initial flood event (F1). Forty‐one days later, we simulated a second flood event (F2) on the three replicate plots in the flood treatment that experienced two flood sedimentation events in a single rain season. These plots had a second series of high frequency sampling for the first 37 days after F2. Subsequent to this time point, all of the plots were sampled less frequently to track the long term recovery of the intertidal ecosystem. During each time point, 8 random core samples were collected from each of the experimental and control plots. Five of these cores were used for subsequent macrofaunal community analysis (Objective 2) and three cores for benthic habitat physical properties (Objective 3). This high frequency sampling (13 time points in year one) and field days required (>60 days) in this first year has led to incomplete analyses of many of the collected samples. Therefore, our descriptions of results for Objectives 2 and 3 should be viewed as preliminary. However, there are definitely some clear patterns that we have observed to date. Additional data collection at the study sites in year one included: tidal currents using a Sontek acoustic doppler velocimeter (ADV) deployed on a benthic tripod, porosity profiles of the study plots during the first 30 days using an in situ resistivity profiler (IRP), and intermittent sediment trays used for xradiography of sediment and burrow structure over the course of the study.
Objective 2: Track the impact of sediment stress on the intertidal benthic community
The macrofauna cores were sectioned into three depth intervals (0‐2, 2‐6, 6‐12 cm) permitting us to vertically separate flood impacts among shallow and deep dwelling species. Sample processing for macrofauna is a four step process including sieving and transferring, sorting into broad taxonomic categories (e.g. amphipods, polychaetes, etc.), and taxonomic identification of species in the sample. The last step also includes taxonomic verification of identified species by professional taxonomists. The last taxonomic identification stage is the most time‐intensive and our data to date is limited by incomplete coverage and replication. Even so, there are clear patterns that we have observed in the study to date.
The infaunal benthic community is composed of at least 24 taxonomically verified species. The benthic community is dominated numerically by crustaceans, especially the tanaid Leptochelia dubia, 5 corophiid amphipod species, and other gammarid amphipods. These three groups account for over 90% of the abundance in the top 0‐6 cm across the study area. In contrast, the deeper‐dwelling community (6‐12 cm) is dominated by polychaetes, primarily the capitellid Mediomastus californiensis. The limited flood impacted samples we have analyzed were from the initial (F1) flood sedimentation event. The flood deposits had an immediate negative effect on the benthos in the flood plots relative to controls. We attributed the initial decrease in abundance and diversity measured in the experimental plots to the mobile behavior of the shallow dwelling crustacean community (gammarid amphipods, tanaids, and cumaceans) rather than direct mortality. Direct (density decreases in surface layers, surface traces) and indirect (burrow traces in x‐radiographs) observations indicated that they left the flood plots leaving the less mobile, deeper dwelling (6‐12 cm) species behind. However, many of the mobile crustacean species, especially the tanaids and corophiid amphipods, rapidly recolonized the flood layers over a 3‐4 month period. The dataset is not yet robust enough to go beyond these general observations of the benthic community, but our initial results highlight the potential importance of species traits (e.g., mobility or behavior) in determining community response and resilience to rapid sedimentation disturbance events.
Objective 3: Track changes in benthic habitat physical properties
This study includes extensive documentation and measurement to changes in the benthic habitat in parallel with the extensive macrofaunal measurements. This includes extensive photo documentation of changes to the plots, core collection for a suite of sediment physical properties (total organic carbon, sediment chlorophyll, grain size, porosity), and measurement of oxygen dynamics in response to flood sedimentation events.
Visually, our observations of the plots show the presence and persistence of the flood layer throughout the first 157 days of the experiment in year one. Despite high current speeds measured at the site by the ADV, the 3‐5 cm flood layers deposited during the flood events were not eroded. These observations highlight the persistence of the flood sedimentation disturbance and the potential longterm effects on the intertidal ecosystem. These visual changes and impacts were also observed in the physical properties datasets. For example, the total organic carbon (TOC) profiles measured before, during, and 2 days after the F1 flood showed a dramatic spike in TOC to 1.6%, 7 times the values found in the surface sediments of the controls. With the large number of field days from January to July, many of the other physical property datasets are too incomplete to report here. Completing these analyses is a major goal of year 2 of the project (see below).
One of the cores collected in each replicate study plot was used to measure microsensor profiles of oxygen, incubations for sediment oxygen demand, and benthic photosynthesis measurements. These measurements permit us to compare the gradients and penetration of oxygen among the experimental treatments that may be indicative of stressful conditions for the benthos, and assess flood impacts on the benthic microalgal community which can oxygenate surface sediments and provide food resources to the remaining benthos in the flood plots. Examination of a time series of oxygen and benthic photosynthesis over 14 days in both control and flood plots showed a clear impact on benthic microalgal photosynthesis, but an unexpectedly low impact on oxygen gradients and penetration. In flood plots, microalgal photosynthesis was absent or greatly reduced when compared to the control plots which showed classic benthic microalgal photosynthesis profiles with 3‐fold increases in both oxygen concentrations and penetration depths. The most surprising result was the relatively deep penetration of oxygen in the flood plots. Despite the 7‐fold increase in TOC noted above, there was little response
by sediment microbial communities. Thus, it is likely that the addition organic carbon present in the flood sediments is refractory and a poor food source for the remaining and recruiting benthos in the flood treatments. This comprehensive understanding of the physical, chemical, and biological characteristics of the benthic habitat will permit us to more accurately interpret the patterns in the macrofaunal response to flood sediment disturbance and highlights the importance of this approach to benthic community studies.
Objective 4: Synthesize datasets and develop framework for predicting resilience of ecosystems
As noted above, most of our effort in year 1 was committed to the implementation of our field study (Objective 1) and collection of extensive benthic macrofaunal (Objective 2) and sediment property (Objective 3) datasets. Synthesis of these data sets will begin in year two but most of the effort in addressing this objective will be in year 3 of the project.

Future Activities:

Research Objective 1:
We will complete the field sampling through 470 days post‐flood for all of the experimental and control plots in Year 2. This will complete Objective 1.
Research Objective 2:
Taxonomic identification of the macrofaunal samples will continue with a goal to complete a statistically robust dataset for the first 37 days after the F1 flood event. As the macrofauna datasets are completed, we will begin the community multivariate analyses. These analyses will be updated and rerun as new time points are fully identified.
Research Objective 3:
We plan to continue the analysis of all types of the sediment samples (porosity, TOC, sediment chlorophyll, and grain size) to parallel the macrofaunal datasets. This will include the intercalibration of fluorimetric and HPLC measurements of sediment chlorophyll to establish the appropriate technique we will use on these samples. The data from the microelectrode and incubation cores are collected but require extensive data post‐processing before full analysis. We will complete these two steps for the oxygen dynamics at the site through day 72 of the F1 flood. Finally, we will complete the data processing for the IRP and Sontec ADV measurements from year 1, and complete the sediment xradiography post‐processing.
Research Objective 4
We will begin the process of synthesizing of the biological, geochemical, geological, and physical datasets in year 2. However, the extensive analytical work still to be completed for Objectives 1 & 2 will likely result in the data synthesis component of the study being moved to year 3.
Dissemination of Results
We plan to begin presenting result of this study at professional conferences. Two are planned for 2009: Marine Benthic Ecology Meetings in Corpus Christi, TX, and the Coastal and Estuarine Research Federation Biennial Meeting in Portland, OR. We will also be sharing results of the study with other PI’s at the STAR Progress Meeting planned for May or June in Seattle, WA.

Journal Articles:

No journal articles submitted with this report: View all 4 publications for this project

Supplemental Keywords:

EPA Region 10, Ecosystems, global climate change, Oregon (OR), pacific coast, pacific northwest, northwest, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystem, Aquatic Ecosystems & Estuarine Research, Ecological Risk Assessment, Ecology and Ecosystems, Environmental Monitoring, climate change, climate, climatic influence, ecosystem, coastal ecosystems, ecosystem indicators, ecosystem stress, environmental measurement, environmental stress, estuaries, global change, marine science, biology, ecology, benthos, estuary, marine, community ecology
, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, climate change, Air Pollution Effects, Monitoring/Modeling, Regional/Scaling, Environmental Monitoring, Ecological Risk Assessment, Atmosphere, coastal ecosystem, biodiversity, environmental measurement, ecosystem assessment, meteorology, global change, greenhouse gases, anthropogenic, climate models, UV radiation, water quality, environmental stress, coastal ecosystems, flood trends, ecological models, climate model, Global Climate Change, land use, regional anthropogenic stresses, atmospheric chemistry, stressor response model

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Progress and Final Reports:

Original Abstract
  • 2007 Progress Report
  • 2009 Progress Report
  • Final Report