Water Quality Monitoring in Bermuda

Introduction

It has long been acknowledged that moorings, anchoring, dredging, and dock construction have impacted Bermuda’s inshore seagrass beds but recently it has been recognized that the extensive offshore beds are also in decline. In 2004, intensive site surveys and mapping of Bermuda seagrass meadows, by the Bermuda Reef Ecosystem Assessment and Mapping Programme (of the Bermuda Biodiversity Project), documented a loss of about one-quarter of the total area estimated from aerial images taken in 1997. Other minor studies indicate a significant loss of seagrass area began about 1995 and was precipitous between then and 1997; however, recent observations suggest this loss is ongoing. This decline did not occur uniformly across the Bermuda platform - and massive loss of area was only apparent in meadows far from shore, which we think are removed from local anthropogenic impacts.

There are no comprehensive data or information we can use to explain this decline, in particular there are no applicable data on nutrients, temperature, and light penetration for any of the beds for periods relevant to the onset of seagrass decline.

Water quality and physical characteristics of the water column are among the ultimate limiting conditions for the presence of seagrass. Transmission of light, temperature and the presence of adequate nutrients can all determine survival of a seagrass bed. Mean salinity, salinity variability, light transmission, and mean nutrient concentrations are important predictor variables to models of landscape-scale changes of marine benthic habitats (Fourqurean et al. 2003. Ecological Applications 13: 474-489). Nutrient levels in the seagrass habitat, which includes both pore water and water column, are the primary driving factors to degradation of seagrass beds in the conceptual model of seagrass community dynamics, which underlies this program.

It has been clearly outlined in the Bermuda Seagrass Conservation and Management Plan that comprehensive water quality monitoring is an essential component of overall management of seagrass habitats in Bermuda. Such a program did not exist in Bermuda until the Government initiated their seagrass habitat studies. The water quality monitoring program also can provide useful data to other management and monitoring issues in the marine environment, including tracking terrestrial runoff and ground water and their significance to nutrient loading.

Field protocols for water quality sampling

Water quality samples are collected by staff of the Bermuda Department of Conservation Services on a monthly basis, over a period of 1-3 days, from 17 permanent monitoring stations are sampled. Surface water samples are collected to determine water column nutrient (dissolved inorganic (DI) nitrate/nitrite, ammonium, reactive phosphorus, Total N, Total P, silicate, DI carbon) and chlorophyll a concentrations. At the same time, PAR attenuation profiles are obtained for the whole water column, salinity, oxygen and turbidity values are collected for surface waters.