ECOLOGY OF BUZZARDS BAY: An Estuanne Profile 



29 



3.1. FreshWater: Rain, 



Surface, and 



Groundwater Flows 



The watershed of Buzzards Bay is that region 

 on which rainfall flows over the surface or through 

 groundwater into the bay. In simplest tenns, the fates 

 of precipitation on the land surface are surface wa- 

 ter runoff through rivers and streams, subsurface 

 transport and discharges as groundwater, or return 

 to the atmosphere via surface evaporation or up- 

 take and loss by plants as evapotranspiration. The 

 partitioning of flow between these various pathways 

 has important consequences for nutrient and pol- 

 lutant transport to and the salinity structure of bay 

 waters. However, accurate partitioning for each 

 embayment is complex and requires diverse long- 

 term data sets and therefore has yet to be performed 

 throughout this system. Measurements of ground- 

 water discharges are also very limited and are con- 

 founded since many of the rivers and streams have 

 significant groundwater contributions. However, 

 rainfall has been measured over the long term at 

 several locations around the watershed and limited 

 river discharge data are available. Based on these 

 data, it is possible to generate a general baywide 

 picture of freshwater inputs. Given the highly per- 

 meable soils resulting from glacial outwash, signifi- 

 cant amounts of fresh water reach the bay directly 

 as groundwater discharge, and the rivers and 

 streams around the bay have a significant base flow 

 (groundwater) component to their discharges. Gla- 

 ciation has also affected discharge, as the western 

 shore with its extensive outwash soils contains the 

 major surface water flows to the bay, primarily along 

 outwash channels. In contrast, the smaller water- 

 shed area and different deposits on the eastern shore 

 yield an area dominated by smaller, generally ground- 

 water-fed streams and direct groundwater 

 discharges (Fig. 3. 1, Table 3. 1). 



Precipitation is relatively uniform throughout the 

 year with only a minor low during summer (Fig. 

 3.2A). However, this temporal uniformity in rain 

 input does not translate into a constant freshwater 

 input to Buzzards Bay. The temporal lag between 



41°30' 



41°20- 



7(ft0' 



7<f30' 



Fig. 3.1. Drainage basins and location of major 

 streams emptying into Buzzards Bay. Westport River 

 (A) has the only long-term stream gauge in the region 

 Numbers refer to rivers listed in Table 3.1. From 

 Signell(1987) 



7a£>/e 3.1. Estimated freshwater flows to Buzzards 

 Bay Numbers refer to locations of rivers on watershed 

 map (Fig. 3.1) Adapted from Signell (1987). 



Contri- 

 Drainage Inferred bution 

 Map area basin flow of flow 

 symbol River (km 2 ) (m ] /s) (%) 



