Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors

Abstract

We developed an algorithm for calculating habitat suitability for seagrasses and related submerged aquatic vegetation (SAV) at coastal sites where monitoring data are available for five water quality variables that govern light availability at the leaf surface. We developed independent estimates of the minimum light required for SAV survival both as a percentage of surface light passing through the water column to the depth of SAV growth (PLW min ) and as a percentage of light reaching leaves through the epiphyte layer (PLL min ). Values were computed by applying, as inputs to this algorithm, statistically derived values for water quality variables that correspond to thresholds for SAV presence in Chesapeake Bay. These estimates of PLW min and PLL min compared well with the values established from a literature review. Calculations account for tidal range, and total light attenuation is partitioned into water column and epiphyte contributions. Water column attenuation is further partitioned into effects of chlorophyll a (chl a), total suspended solids (TSS) and other substances. We used this algorithm to predict potential SAV presence throughout the Bay where calculated light available at plant leaves exceeded PLL min . Predictions closely matched results of aerial photographic monitoring surveys of SAV distribution. Correspondence between predictions and observations was particularly strong in the mesohaline and polyhaline regions, which contain 75-80% of all potential SAV sites in this estuary. The method also allows for independent assessment of effects of physical and chemical factors other than light in limiting SAV growth and survival. Although this algorithm was developed with data from Chesapeake Bay, its general structure allows it to be calibrated and used as a quantitative tool for applying water quality data to define suitability of specific sites as habitats for SAV survival in diverse coastal environments worldwide.

Unexpected resurgence of a large submersed plant bed in Chesapeake Bay: Analysis of time series data

“…Thus, decreases in particulates, possibly the result of reduced nutrient loading, may have been responsible for improved water clarity. Furthermore, in tidal freshwater regions of Chesapeake Bay, epiphytes can contribute 20-60% additional shading beyond light attenuation by dissolved and suspended material in the water column (Kemp et al 2004). Thus, reductions in nutrient loading may have also limited the growth of epiphytes, allowing more light to reach the SAV leaf surface.…”

“…Linear regression results for transition (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) and stable (1984-1998; 2009-2010) estimated that PLB was , 27% during the dry period and , 25% after the dry period (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010). The light threshold for tidal freshwater SAV in Chesapeake Bay is , 13-14% (Dennison et al 1993;Kemp et al 2004); however, this threshold generally applies to existing SAV beds rather than to initiation of a new bed. The fact that our estimated threshold is greater supports the idea that new SAV growth requires more light than an already established bed.…”

“…2, 4). N loading was also increasing; and, consequently, chronic eutrophication led to poor water quality and widespread SAV loss (Bayley et al 1978;Kemp et al 1983Kemp et al , 2005. Tropical Storm Agnes then pushed the already deteriorating SAV system beyond its ''tipping point'' into a degraded state in 1972.…”

“…Seagrass and associated submersed aquatic vegetation (SAV) communities, in particular, undergo episodes of decline and recovery that span seasons to multiple decades. Reports of decline dominate the literature, with many examples of SAV loss attributed to chronically degraded water quality associated with eutrophication (Kemp et al 1983) or extreme weather events such as hurricanes, flooding, and temperature stress (Preen et al 1995). Recent studies, however, have also reported instances of SAV recovery.…”

“…50 km 2 ). Whereas an extreme flood event apparently triggered the historic demise of SAV at Susquehanna Flats, the extended lack of recovery is puzzling because it appears that environmental conditions have generally satisfied the habitat requirements for SAV in oligohaline regions of Chesapeake Bay since water quality monitoring began in 1984 (i.e., April-October median light attenuation coefficient , 2.0 m 21 , total suspended solid and dissolved inorganic phosphorous concentrations , 15 mg L 21 and 0.67 mmol L 21 , respectively; Dennison et al 1993;Kemp et al 2004).…”