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The Water Institute produces a range of scientific publications. In this way, we contribute to the state of the science, communicating cutting edge ideas to a broad technical audience.

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Evaluation of Sediment Diversion Design Attributes and Their Impact on the Capture Efficiency

posted on 02.02.2016

Ehab Meselhe, Author

Many riverine systems have been disconnected from their receiving basins by flood-protection levees and other engineered systems. Reconnecting these alluvial rivers with their receiving basins is a viable option to nourish and sustain existing coastal wetland systems as well as to build new land. This sediment nourishment can be accomplished through direct dredging and placement or through sediment diversions. Efficient design of sediment diversions is important to maximize the land building potential. This study’s objective is to quanti- tatively identify key design attributes of sediment diversions, influencing their ability to capture sediment. The outfall channel alignment angle (ϕ), intake invert elevation, and diversion size are hypothesized as key parameters. The analysis is limited to sediment grain sizes larger than 63 μm and has been performed using a validated three-dimensional numerical model. Click here to view the full publication. 

Influence of the Mississippi River on Pseudo-Nitzschia spp. Abundance and Toxicity in Louisiana

posted on 08.22.2016

Melissa Baustian, Author

Melissa Baustian co-authored "Influence of the Mississippi River on Pseudo-nitzchia spp. Abundance and Toxicity in Louisiana Coastal Waters". The presence of domoic acid (DA) toxin from multiple species of Pseudo-nitzschia is a concern in the highly productive food webs of the northern Gulf of Mexico. The report documents the Pseudo-nitzschia presence, abundance, blooms, and toxicity over three years along a transect ∼100 km west of the Mississippi River Delta on the continental shelf.

 

Application of Species Distribution Models to Identify Estuarine Hot Spots for Juvenile Nekton

posted on 12.14.2016

Ann Hijuelos, Author

Modeling the distribution and habitat capacities of key estuarine species can be used to identify hot spots, areas where species density is significantly higher than surrounding areas. This approach would be useful for establishing a baseline for evaluating future environmental scenarios across a landscape. We developed species distribution models for early juvenile life stages of brown shrimp (Farfantepenaeus aztecus), white shrimp, (Litopenaeus setifurus), blue crab (Callinectes sapidus), and spotted seatrout (Cynoscion nebulosus) in order to delineate the current coastal hot spots that provide the highest quality habitat conditions for these estuarine-dependent species in Louisiana. Response curves were developed from existing long-term fisheries-independent monitoring data to identify habitat sustainability for fragmented marsh landscapes. Response curves were then integrated with spatially explicit input data to generate species distribution models for the coastal region of Louisiana. Using spatial auto-correlation metrics, we detected clusters of suitable habitat across the Louisiana coast, but only 1% of the areas were identifies as true hot spots with the highest habitat quality for nekton. The regions identifies as hot spots were productive fringing marsh habitats that are considered the most vulnerable to natural and anthropogenic impacts. The species distribution models identify the coastal habitats which currently provide the greatest capacity for key estuarine species and will be used in the Louisiana coastal planning process to evaluate how species distributions may change under various environmental and restoration scenarios. Click here to view the full publication. 

Hydrologic Modeling in a Marsh–Mangrove Ecotone: Predicting Wetland Surface Water and Salinity Respo

posted on 09.17.2015

Ehab Meselhe, Author

At the fringe of Everglades National Park in southwest Florida, United States, the Ten Thousand Islands National Wildlife Refuge (TTINWR) habitat has been heavily affected by the disruption of natural freshwater flow across the Tamiami Trail (U.S. Highway 41). As the Comprehensive Everglades Restoration Plan (CERP) proposes to restore the natural sheet flow from the Picayune Strand Restoration Project area north of the highway, the impact of planned measures on the hydrology in the refuge needs to be taken into account. The objective of this study was to develop a simple, computationally efficient mass balance model to simulate the spatial and temporal patterns of water level and salinity within the area of interest. This model could be used to assess the effects of the proposed management decisions on the surface water hydrological characteristics of the refuge. Click here to view the full publication. 

Climate Change in the Holocene

posted on 09.04.2015

Mead Allison, Author

Information derived from natural sources such as tree rings and lake sediments can tell us about the weather and climate millions of years ago (palaeoclimate). Studying past climates on Earth is not only important to build a picture of the past, but also to address current climate change. Understanding whether similar changes have happened previously and how they were brought about can help scientists understand if these same forces are causing climate change today, and make predictions about what may happen in the future. Click here to view the full publication. 

Sources of organic matter in sediments of the Colville River delta, Alaska: A multi-proxy approach

posted on 08.13.2015

Mead Allison, Author

Thawing of permafrost and subsequent release of organic carbon in the warming Arctic has great potential to influence carbon cycling between the land and ocean. Here, we investigated temporal and spatial differences of organic carbon sources in sediments of Colville River delta and the adjacent Simpson Lagoon, Alaska (USA) over the last ∼50 years, using a multi-proxy approach (lignin, fatty acids, sterols, bulk and compound-specific 13C isotopes). Stations closer to the river mouth showed greater inputs of soil and litter-derived terrestrial material based on the terrestrial inputs indicator (Λ8), soil biomarker (3,5-Bd), and degradation index ([Ad/Al]v), as well as stronger and more frequent watershed-flushing events, coupled with Colville River discharge events, than stations in the lagoon. Values of Λ8, 3,5-Bd, and [Ad/Al]v in sediments ranged from 0.75–2.69, 0.02–0.44 mg/100 mg OC, and 0.23–0.85, respectively. The increase of terrestrial inputs in sediments near the delta for the last ∼50 years is most likely due to increase of river discharge under warmer temperatures in recent decades. Coastal erosion and inputs from other river sources (e.g., Kuparuk and Mackenzie Rivers) also contribute to the organic carbon in sediments of the delta. Rudimentary fatty acid indices reflected two distinct groups of bacteria in these sediments. Additionally, the sterol biomarker 24-ethylcholest-5-en-3β-ol is useful to track peat inputs in the Arctic. Click here to view the full publication. 

An Examination of Froude-Supercritical Flows and Cyclic Steps On A Subaqueous Lacustrine Delta, Lake

posted on 08.13.2015

Mead Allison, Author

Density-driven submarine flows, including turbidity currents, play an important role in the transfer of sediment into deep water. These bottom-hugging flows often produce flow-transverse bedforms along their path. A sedimentological and geophysical survey of the Stehekin River delta in Lake Chelan, Washington, reveals a downslope-elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the Stehekin River. An analysis of the bedform morphologies, delta geometry, and density contrast between lake and river water suggests that these hyperpycnal flows are Froude-supercritical. The bedforms are likely cyclic steps, flow-transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes. The ability to examine the three-dimensional bed configuration produced by natural density-driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes. Click here to view the full publication. 

High rates of organic carbon burial in fjord sediments globally

posted on 05.05.2015

Mead Allison, Author

The deposition and long-term burial of organic carbon in marine sediments has played a key role in controlling atmospheric O2 and CO2 concentrations over the past 500 million years. Marine carbon burial represents the dominant natural mechanism of long-term organic carbon sequestration. Fjords—deep, glacially carved estuaries at high latitudes—have been hypothesized to be hotspots of organic carbon burial, because they receive high rates of organic material fluxes from the watershed. Here we compile organic carbon concentrations from 573 fjord surface sediment samples and 124 sediment cores from nearly all fjord systems globally. We use sediment organic carbon content and sediment delivery rates to calculate rates of organic carbon burial in fjord systems across the globe. We estimate that about 18 Mt of organic carbon are buried in fjord sediments each year, equivalent to 11% of annual marine carbon burial globally. Per unit area, fjord organic carbon burial rates are twice as large as the global ocean average, and fjord sediments contain twice as much organic carbon as biogenous sediments underlying the upwelling regions of the ocean. We conclude that fjords may play an important role in climate regulation on glacial–interglacial timescales. Click here to view the full publication. 

Linking the bottom to the top in aquatic ecosystems: mechanisms and stressors of benthic-pelagic co

posted on 05.01.2015

Melissa Baustian , Author

Linkages between benthic and pelagic habitats occur in both freshwater and marine systems across multiple spatial and temporal scales, and are influenced by a number of chemical, biological, and physical forces. We identified three major mechanisms of benthic-pelagic coupling: (1) organism movement, (2) trophic interactions, and (3) biogeochemical cycling. We also explore the implications of several stressors, including invasive species and climate change that will inevitably impact the linkages between benthic and pelagic habitats. We identify critical research gaps that need to be addressed to quantify the habitat coupling of these ecosystems. We advocate for more collaboration among scientists with expertise in benthic and pelagic habitats in both freshwater and marine ecosystems to fully understand the cycles, interactions, processes, and functions of benthic-pelagic coupling in ecosystems. Finally, we suggest targeted research needs for better capturing of cross-ecosystem linkages in aquatic ecology. Click here to view the full publication. 

Proposed best modeling practices for assessing the effects ofecosystem restoration on fish

posted on 03.17.2015

Denise Reed, Shaye Sable, et al., Author

Large-scale aquatic ecosystem restoration is increasing and is often controversial because of the economic costs involved, with the focus of the controversies gravitating to the modeling of fish responses. This paper presents a scheme for best practices in selecting, implementing, interpreting, and reporting of fish modeling designed to assess the effects of restoration actions on fish populations and aquatic food webs. Previous best practice schemes that tended to be more general are summarized, and they form the foundation for our scheme that is specifically tailored for fish and restoration. Click here to view the full publication.