Early indicators of stress in mangrove forests with altered hydrology in Tampa Bay, Florida, USA

Abstract

Mangroves experience stress or mortality when gas exchange by aerial root structures is hindered by sediment burial or constant inundation. The resulting loss of belowground roots and increased decomposition can lead to a loss of surface elevation through peat collapse, furthering the degree of inundation. This study identified ten live mangrove forests across Tampa Bay (Florida, USA) with stagnant water and/or abundant adventitious root growth (a sign of stress) and compared vegetative, water, and soil characteristics of stressed and reference mangrove forests to identify early indicators of stress and potential peat collapse. Two stressed sites were characterized by sandy, high-density soils and were hypothesized to have been stressed by a burial event. The remaining eight stressed locations had stagnant pools of discolored water with low dissolved oxygen (1.1 ± 1.3 mg L−1). Soil from the hydrologic stress sites had significantly lower dry bulk density than reference mangrove sites (0.24 ± 0.14 g cm−3 vs. 0.40 ± 0.11 g cm−3), greater organic matter composition (49.3 ± 17.2% vs. 26.1 ± 9.0%), and a higher proportion of root material. Salinity and porewater dissolved organic carbon varied widely but were not significantly different between reference and hydrologic stress sites. Altered hydrology due to anthropogenic alteration can often be improved; thus, proactive restoration is recommended to prevent mortality and peat collapse in affected mangrove forests.