Wetland Loss in the Northern Gulf of Mexico: Multiple Working Hypotheses

I examined four hypotheses about causes for the dramatically high coastal wetland losses (0.86% yr−1) in the northern Gulf of Mexico: an extensive dredged canal and spoil bank network, a decline in sediments in the Mississippi River during the 1950s, Mississippi River navigation and flood protection levees, and salinity changes. Natural factors contributing to these habitat changes include eustatic sea-level rise and geological compaction, which appear to have remained relatively constant this century, although variation does occur. These four hypotheses were tested using data on land-to-water changes in 15-min quadrangle maps inventoried for four intervals between the 1930s and 1990. Land loss rates were directly proportional to changes in wefland hydrology in time and space. A linear regression of the direct losses due to dredging versus the losses due to all other factors (indirect losses) had a zero intercept and a slope that increased with time. The ratio indirect:direct land loss was highest nearest the estuarine entrance. The coastwide patterns of land loss do not appear to be affected by riverine sediment reductions over the last 60 yr. The effects of changes in wetland hydrology from dredging human-made channels and forming dredged spoil banks appear to be the most efficacious hypothesis explaning these dramatic losses. The effects of extensive human-induced changes on this coast have apparently overwhelmed the causal linkages identified in the historical re-constructionist view of deltaic gain and loss that emphasizes the role of mineral sediments. A paradigm shift is therefore proposed that emphasizes a broad ecological view as contrasted to a mostly physical view emphasizing the role of sediment supply in wetland maintenance. In this view, plants are not an ancillary consequence of strictly geological dynamics such as sediment supply but are dominant agents controlling factors relevant to coastal restoration and management efforts

Just Us

Introduction: A thorough understanding of ecology is a necessity as the Earth becomes crowded, there is more intense resource use and exhaustion, and the exposure to pollutants has diversified. Outcomes: Everyone must be involved as we develop the moral compass and maps for a desirable world. The transition will be made within the context of complex social forces, which must be engaged in purposeful collaboration and action. All individuals have the embryonic need and possess diverse abilities to contribute to the transcendence of problems arising from the human response to social inequities. Discussion: These will be difficult and nuanced transitions. One example is the Balinese water distribution system, whose site-specific adjustments developed over thousands of years. Examples from country-to-country comparisons show that Eco-civilizations, to be \u27civil\u27, must be fair, inclusive, and joyful, and more than about misleading metrics like Gross Domestic Product, individuality, material accumulations and competition. Conclusion: We are in this together; it is not \u27them or us\u27 - it is only \u27Us\u27

Discussion Of: Olea, Ra And Coleman, Jl, Jr., 2014. A Synoptic Examination Of Causes Of Land Loss In Southern Louisiana As Related To The Exploitation Of Subsurface Geological Resources. Journal Of Coastal Research, 30(5), 1025-1044.

I comment on Olea and Coleman\u27s (2014) conclusion that subsidence was the primary cause of the dramatic rise in Louisiana\u27s coastal land losses in the last 100 years. The focus on subsidence combined with the omission of context for factors not related to subsidence (e.g., dredged canals), leaves the reader with the incorrect conclusion that anthropogenic factors observed to date are insignificant, and that coastal wetland losses are only driven by subsidence. I address this omission by discussing two points about anthropogenic influences: (1) dredged canals and (2) changes in sediment load from the watershed and its distribution. They omit quantitative inclusion of two signature symptoms of the cause-and-effect relationships at temporal and spatial scales. To whit, there are: direct relationships between canal density and land loss over decades and shorter intervals for the whole coast and individual estuaries, instances of indirect losses immediately after canal construction, an increase in ponding near dredged canals but not further away, and, evidence of effective hydrologic barriers created by the spoil bank above- and belowground. The view that geological subsidence exerts a top-down control on the net adjustment to changes in vertical space leads to the narrow view of restoration being modeled using the mineral soils for wetland soils comprised mostly of organics. Further, the decline in suspended sediment concentrations since the 1950s (from dam construction) needs to be put within the context of the landscape changes occurring when European colonization resulted in much higher rates of erosion. The restriction of exclusively geological factors driving land loss is, therefore, an incomplete view of what causes land loss in modern times and a perhaps dangerously naive basis for management decisions on this coast. I agree with their conclusions that (1) geological subsidence has not changed significantly in the last 100 years, (2) fluid withdrawal is an unlikely and unproven large enough force to cause the patterns in land loss across the deltaic plain, and (3) acceleration in sea level rise will rise to problematic levels in the near future

Coastal Wetland Subsidence Arising From Local Hydrologic Manipulations

Twenty-three estimates of soil subsidence rates arising under the influence of local hydrologic changes from flap-gates, weirs, dikes, and culverts in tidal wetlands were compared to 75 examples of subsidence in drained agricultural wetlands. The induced subsidence rates from these hydrologic modifications in tidal wetlands can continue for more than 100 years, and range between 1.67 to 0.10 cm yr−1 within 1 to 155 years after the hydrologic modifications commence. These subsidence rates are lower than in freshwater wetlands drained for agricultural purposes, decline with age, and are significant in comparison to the rates of global sea level rise or the average soil accretion rates. The elevation change resulting from local hydrologic manipulations is significant with respect to the narrow range of flood tolerances of salt marsh plants, especially in microtidal environments

Will Lowering Estuarine Salinity Increase Gulf of Mexico Oyster Landings?

Previous studies provide conflicting opinions on whether lower than average salinities in Gulf of Mexico (GOM) estuaries are likely to increase or decrease oyster harvests (Crassostrea virginica), which represented 69% and 54% of the United States oyster landings by weight, and dockside value, respectively, in 2003. The present study examined a 54-yr record (1950–2003) of oyster harvests and river discharge in five major estuaries in GOM states (Florida, Alabama, Mississippi, Louisiana, and Texas). Oyster landings were inversely related to freshwater inflow. Peaks in landings, 21 of 23 in West Florida, Alabama, Mississippi, and Texas combined, were coincidental with lows in river discharge from the major rivers in the estuaries. Lows in landings in these states (17 of 19) coincided with peaks in discharge of the major rivers feeding their estuaries. Landings in Breton Sound, Louisiana, were also inversely related to river discharge. The only exception to this pattern was for landings in the Plaquemines Parish, Louisiana, part of the Breton Sound estuary, where there were higher landings following increased Mississippi River discharge. The Bonnet Carré spillway, completed in 1931, diverts flood waters from the Mississippi River to Lake Pontchartrain, and it has been opened to reduce flood heights in 1937, 1950, 1973, 1975, 1979, 1983, and 1997. Twenty-five of 28 times after the spillway was opened, oyster landings in Mississippi were lower than in the other four states. The inverse relationship between freshwater inflow and oyster landings suggests that the proposed Bonnet Carré Freshwater Project, designed to reduce estuarine salinity, cannot be justified on the basis of anticipated higher oyster yields in Mississippi or Louisiana. Manipulating estuarine salinity in the GOM should be done within the context of the whole estuary and not just part of the estuary

Element Ratios and Aquatic Food Webs

Organic matter is the result of concentrating a few non-metals that are relatively rare in the earth’s crust. Most of these essential elements are in a rough proportionality within phylogenetic groupings. Life is thus working against a concentration gradient to extract or accumulate these elements, and this metabolic work is accomplished in interrelated and often subtle ways for many other elements. The physiological requirement to sustain these elemental ratios (commonly discussed in terms of the N∶P ratios, but also C∶N, C∶P, and Si∶N ratios) constrains organization at the cellular, organism, and community level. Humans, as geochemical engineers, significantly influence the spatial and temporal distribution of elements and, consequently, their ratios. Examples of these influences include the changing dissolved Si: nitrate and the dissolved nitrate: phosphate atomic ratios of water entering coastal waters in many areas of the world. Human society may find that some desirable or dependent ecosystem interactions are compromised, rather than enhanced, as we alter these elemental ratios. Human-modulated changes in nutrient ratios that cause an apparent increase in harmful algal blooms may compromise the diatom-zooplankton-fish food web. It will be useful to improve our understanding of aquatic ecosystems and for management purposes if the assiduous attention on one element (e.g., N or P) was expanded to include the realities of these mutual interdependencies

Comments on Buzan et al. “Positive Relationships between Freshwater Inflow and Oyster Abundance in Galveston Bay, Texas”

Buzan et al. critique Turner’s (Estuaries and Coasts 29:345–352, 2006) analysis of the relationship between freshwater inflow and oyster productivity in the Gulf of Mexico, using 16 years of fisheries-independent data for Galveston Bay. They conclude that the catch-per-unit effort (CPUE; number h−1) of marketable oysters increase 1 to 2 years after years with increased freshwater inflows, and they express concerns that water supply managers may mis-apply the results of Turner (Estuaries and Coasts 29:345–352, 2006) to justify a reduced freshwater inflow to Galveston Bay. I find no relationship between the CPUE of oyster spat or marketable oyster density and the commercial harvest, but do find a strong inverse relationship between harvest and river discharge in Galveston Bay. There are three possible factors that may explain why the annual variations in the fisheries-independent data are not coherent with the annual variations in commercial harvest: variable levels of water quality, inconsistent fishing effort, and the fact that the fisheries-independent data are not prorated for the area of the reefs actually fished. I concur, completely, with the apprehension that reductions in freshwater inflow will be implemented without examining the full set of assumptions and consequences, and thereby compromise estuarine ecosystem quality, and perhaps permanently, before mistakes can be seen or reversed

Of Manatees, Mangroves, and the Mississippi River: Is There an Estuarine Signature for the Gulf of Mexico?

Important parameters of estuarine variability include morphology, flushing times, nutrient loading rates, and wetland: water ratios. This variability both reflects and disguises underlying relationships between the physics and biology of estuaries, which this comparative analysis seeks to reveal, using the Gulf of Mexico (GOM) estuaries as a starting point. A question used to focus this analysis is: are the GOM estuaries unique? The GOM receives the Mississippi River, a uniquely large, world-class river, which dominates the freshwater and nutrient inflows to the GOM continental shelf, whose margins include 35 major estuarine systems. These GOM estuaries have 28% and 41% of the U.S. estuarine wetlands and open water, respectively. Within the GOM, estuarine nitrogen, phosphorus, and suspended matter loading varies over 2 orders of magnitude. Anoxic estuarine events tend to occur in estuaries with relatively slow freshwater turnover and high nitrogen loading. Compared to estuaries from other regions in the U.S., the average GOM estuary is distinguished by shallower depths, faster freshwater flushing time, a higher wetland area:open water area ratio, greater fisheries yield per area wetland, lower tidal range, and higher sediment accumulation rates. The average GOM estuary often, but not always, has a flora and fauna not usually found in most other U.S. estuaries (e.g., manatees and mangroves). Coastal wetland loss in the GOM is extraordinarily high compared to other regions and is causally linked to cultural influences. Variations in nutrient loading and population density are very large among and within estuarine regions. This variation is large enough to demonstrate that there are insufficient systematic differences among these estuarine regions that precludes cross-system analyses. There are no abrupt discontinuities among regions in the fisheries yields per wetland area, tidal amplitude and vegetation range, salt marsh vertical accretion rates and organic accumulations, nitrogen retention, or wetland restoration rates. These results suggest that a comparative analysis emphasizing forcing functions, rather than geographic uniqueness, will lead to significant progress in understanding how all estuaries function, are perturbed, and even how they can be restored

Sustainability: More About The Toolmaker Than The Tools

A sustainable system is not necessarily a high-quality one, but it could be. We could, for example, “survive” on the desperate edge, as the remnants in a self-fouled and deteriorating environment. Why won’t a future sustainable system be just another industrial model of mass efficiency and throughput? Perhaps the incompatible outcomes are a choice between the sometimes nearly invisible civilizing aspects of culture nurturing respect, equality, and cooperation on one hand, and the greed and self-indulgences undermining social tolerance, empathy, and cooperation that ends up promoting violence and dehumanization. The human heritage is subtle, indestructible, and worth nurturing if we want that hospitable sustainable system. But, assuming that a kind of social osmosis will be sufficient to sustain justice and fairness is wrongheaded and dismisses the historical examples. A new cultural narrative is needed to override the maladaptive dissonance preventing formation of sustainable systems. This narrative will be anchored in personal initiatives, incorporates an appreciation of our evolved heritage, and is informed by intentional social learning within groups and occasional social punishment

Smaller Size-At-Age Menhaden With Coastal Warming And Fishing Intensity

The size-at-age of one million Brevoortia tyrannus and B. patronus, harvested from Maine to Texas over 65 years, were analysed to determine if there was evidence of changes consistent with the well documented temperature size rules. The average annual weight and length for age 3-, 4- and 5-year-old fish declined on both the Atlantic and Gulf of Mexico (GOM) coasts. For example, the average size of a 4-year-old fish captured in 2010 from the Atlantic and GOM, relative to an average 4-year-old fish captured in 1987, is 15 per cent and 11 per cent lighter, respectively. Small changes in the year-to-year size of same-aged fish were closely related to variations in the annual air temperature (used as a proxy for water temperature) for fish on both coasts. The size-at-age of GOM fish are also smaller during overfished periods compared with underfished periods by 10-24 per cent, and decrease by about the same proportion as indicated by temperature changes. The most plausible explanation for these size changes is that they are a consequence of recent coastal and oceanic warming. These reductions in size-at-age by temperature and fishing pressure affect egg production, oil yield and prey community for one-half of the US Atlantic and GOM fish harvest. The future of menhaden fish size-at-age will be, it seems, smaller as oceanic temperatures rise