Geology topics

Donald R. Cahoon

Publications and source records attributed to Donald R. Cahoon.

94 records · Page 6Linked to original sources

USGS1993

Marsh submergence vs. marsh accretion: Interpreting accretion deficit data in coastal Louisiana

The apparent imbalance between relative sea-level rise and vertical marsh accretion is frequently cited as a major factor in the problem of wetland loss in Louisiana. Rates of relative sea-level rise are high in Louisiana due to high rates of subsidence. Although marsh accretion rates are also high, they are usually insufficient to maintain the relative elevation of the marsh surface. This situation is commonly referred to as an accretion deficit. The interpretation of subsidence and accretion data, and therefrom accretion deficit data, is confounded by the numerous geologic, biologic, and sedimentologic processes influencing coastal marshes in Louisiana. Therefore, calculation of accretion deficits can be influenced by the techniques used to measure subsidence and accretion. The concept of accretion deficit is based on the assumption that accretion rates are equivalent to elevation change rates, but this assumption may not necessarily be correct. We suggest that direct measurements of elevation change in marsh surface can provide better indications of the status of the marsh surface with respect to subsidence and accretion.

Louisiana↗

USGS1989

Mitigating oil and gas impacts in coastal wetlands

This abstract refers to technical recommendations for avoiding, minimizing, and restoring (i.e., mitigating) drilling site access impacts related to oil and gas activities in coastal wetlands through regulatory review, drawing mostly from the Louisiana experience. The two standard methods used to access wetland drilling locations are canals and roads, both of which require dredging. Each access method impacts wetland values and functions and each has been implicated directly and indirectly in wetland loss by converting marsh habitat to open water or upland habitat and by altering the local hydrologic regime. However, numerous regulatory management techniques exist and should be employed to avoids minimize, and restore canal and road-dump impacts.

Conference Paper↗

USGS1989

Structural marsh management research priorities

The paper presents a prioritized list of research issues related to structural marsh management developed by a multidisciplinary panel of regulatory agency representatives, landowners, and scientists. More than 75 issues were identified concerning landscape changes, influence on ecological processes (i.e., hydrologic, biologic, and edaphic factors), habitat quality, cumulative impacts, and management approach. These issues were prioritized and organized around six basic questions regulatory personnel must try to answer for each marsh management plan application. The six questions deal with the influence of marsh management on, in order of most immediate need, marsh loss and health, fisheries, wildlife, habitat change, water quality, and cumulative effects.

Conference Paper↗

USGS1988

Environmental impacts and regulatory policy. Implications of spray disposal of dredged material in Louisiana wetlands

The capabilities of a new wetland dredging technology were assessed along with associated newly developed state and federal regulatory policies to determine if policy expectations realistically match the technological achievement. Current regulatory practices require amelioration of spoil bank impacts upon abandonment of an oil/gas well, but this may not occur for many years or decades, if at all. Recently, a dreding method (high-pressure spray spoil disposal) was developed that does not create a spoil bank in the traditional sense. Its potential for reducing environmental impacts was recognized immediately by regulatory agencies for whom minimizing spoil bank impacts is a major concern. The use of high-pressure spray disposal as a suitable alternative to traditional dreding technology has been adopted as policy even though its value as a management tool has never been tested or verified. A qualitative evaluation at two spoil disposal sites in saline marsh indicates that high-pressure spray disposal may indeed have great potential to minimize impacts, but most of this potential remains unverified. Also, some aspects of current regulatory policy may be based on unrealistic expectations as to the ability of this new technology to minimize or eliminate spoil bank impacts.

Louisiana↗