Pier Shading Assessment

Introduction

As a result of on-going shoreline development and recreational use along Mississippi’s coastal wetlands, valuable marshland is being impacted as attempts are made to access open water from land.  Numerous man-made piers that extend across tidal marshes from small residential properties, although designed for minimum stress on marsh habitats, may still have a considerable cumulative effect on overall salt marsh productivity by blocking light from reaching marsh grass beneath them.  Shading caused by physical aspects of piers, including width, height above the grass, degree of separation between boards, and orientation with respect to angle of the sun, may contribute to diminishing the productivity of affected marsh grass.  The purpose of this project is to evaluate and quantify these aspects of pier construction on marsh productivity by (1) evaluating the long-term effects and extent of existing pier constructions originally surveyed in 2006, and (2) assessing the broader spatial impacts and economic costs associated with various permitted pier dimensions.

Sample piers were selected in the three coastal counties of Mississippi and visited at two time periods (2006 and 2021). We focused on the use of irradiance measurements at pier sites to determine how piers affect the available light environment. Piers of different heights, widths, and board spacing were compared to identify factors that have the biggest effect on shading (Figure 1 and 2). Plant species diversity was documented at each site to compare communities around each pier versus underneath the piers. We found that each height, width, and board spacing can affect the available light underneath piers, with height having the most consistent effect. Analysis on the vegetation community around pier sites did not provide clear results of any broader impacts from the shading effects. The light available underneath piers was measured to be below the irradiance threshold for both Juncus roemarianus and Sporobolus alterniflorus. Potential shading effects may be mitigated by altering construction methods and dimensions. This research is important, as it can tie into management implications directed towards saltmarsh conservation. The specific goals of this research are to:

• Determine if pier shading effects are potentially negatively affecting the salt marsh plants J. roemerianus and S. alterniflorus on the Mississippi Gulf Coast.

• Determine which pier characteristics, height, width, or decking are most pertinent to deleterious pier shading effects and relate findings to management implications.

A research project of the Center for Plant Restoration and Coastal Plant Research - https://sites.google.com/site/coastalplantrestoration/