The Chesapeake Bay as an Estuary: An introduction. Istvan A. Urcuyo Gettysburg College

Transcription

1 The Chesapeake Bay as an Estuary: An introduction. Istvan A. Urcuyo Gettysburg College

2 The Chesapeake Bay -Native Americans resided on its shores since 8000 B.C.

3 The Chesapeake Bay -Original Native American group around the CB were the Powhatans. They left no written records and spoke Algonquian. -Natives called it Chesepiooc [Great Water]. -Native population when first Europeans settlers: st European to enter CB region: Spanish explorer Lucas Vásquez de Ayllón (1524). The Towne of Pomeiooc Source: &

4 The Chesapeake Bay -In 1605, the French started a colony at Port Royal (Annapolis). -In 1607, Jamestown settlement was established on the James River. -In 1608, Captain John Smith was the first European to thoroughly explore and map the Chesapeake Bay. -In 1634, Lord Baltimore established the first English colony in Maryland, known as St. Mary's City. Source: &

5 The Chesapeake Bay -Formed approximately 10,000 years ago during the end of the last ice age. It is a Drowned river valley miles long and its watershed is fed by 19 principle rivers and over 400 lesser creeks. -The Susquehanna, Potomac and James Rivers contribute 80% of the freshwater input. -On average, it holds over 15 trillion gallons of water!

6 The Chesapeake Bay -It has 11,700 miles of tidal shoreline. -It is shallow: average depth of 30 ft in the main stem. -Varies in width from 3.4 miles near Aberdeen MD to 35 miles at its widest point near the mouth of the Potomac. -Semidiurnal tides with a tidal range of 3ft at the mouth of the Bay.

7 The Chesapeake Watershed -50% of the water comes from the Atlantic Ocean, the rest comes from the 64,000 square-mile drainage basin (watershed) which include parts of New York, Pennsylvania, West Virginia, Delaware, Maryland, Virginia and the entire District of Columbia. Image: EPA 903-R

8 Pennsylvania and the Chesapeake Bay -Pennsylvania makes up over 1/3 of the entire watershed, more than any other state. -52% of Pennsylvania is found within the Chesapeake watershed. -The Susquehanna River alone drains 92% of the watershed and another 7% is drained by the Potomac River. -The Susquehanna River has an average flow of 19 million gallons of water per minute and it supplies 50% of the freshwater entering the Bay. Source: The Pennsylvania Chesapeake Bay Program

9 The Chesapeake Watershed -Approximately 16 million people live, work or play in the watershed. -It is estimated that by the year 2020 there will be ~18 million people in the watershed. -The Chesapeake Bay is the LARGEST ESTUARY in the country.

10 What is an Estuary? An estuary is a body of water that is partially surrounded by land and where freshwater mixes with ocean water. -Estuaries are locations of important biological productivity, diversity and ecological significance. -Important physical characteristics of estuaries: Salinity, Light penetration, Temperature and Mixing.

11 Salinity -The total concentration of dissolved inorganic solids in water is its salinity. -Salinity is measured by oceanographers as parts-per-thousands (ppt). -Freshwater contains few salts (< 0.5 ppt) while Ocean water averages 35 ppt.

12 Salinity -Water salinity in the Bay ranges from 30ppt near the mouth to freshwater at the junctions with the rivers. -Salinity increases from the surface to the bottom with deeper waters having up to 3 times the salinity. -Most of the water in CB is brackish water (salinity > 0.5ppt but < 25ppt).

13 Salinity Saltier water is found along the eastern shore due to the influence of the Coriolis Effect and the larger input of freshwater from the western shore.

14 Salinity Salinity in the bay also varies according to the seasons due to differences in total rainfall input. Image: EPA 903-R

15 Light Light is a form of electromagnetic radiation from the Sun. -Visible light is ONLY a portion of the total range. -About 50% of the entering light is absorbed in the first meter of depth and ~80% is absorbed at a depth of 10 meters (33 ft). -Only ~1% of the total light remains in the clearest waters at a depth of ~150 meters.

16 Light The wavelengths of visible light are not transmitted equally. -The long wavelengths (reds) are absorbed rapidly within the first 10 meters. The shorter green-blue wavelengths are transmitted to greater depths. -Open-ocean water is often clear and deep blue.

17 Temperature -The ability of a substance to give up or absorb a given amount of heat and undergo a change in temperature is a measure of the substance s heat capacity (or specific heat). -The heat capacity of water is among the highest of all known common substances. -Water temperatures in the Bay fluctuate dramatically due to its shallow depth. It normally ranges from 34 F in the winter to 84 F in the summer.

18 -Thermocline: region where temperature changes rapidly with depth. -Halocline: region where salinity changes rapidly with depth -Pycnocline: region where density changes rapidly with depth Image: EPA 903-R

19 Types of Estuaries -Salt wedge estuary: this is the simplest type of estuary and it is characterized by the presence of a saltwater wedge occurring near the mouth of the river.

20 Types of Estuaries -Well-mixed estuaries: these are shallow estuaries with a strong tidal mixing and a relatively low river flow. -This combination creates a slow seaward flow of water and a near complete mixing between freshwater and saltwater.

21 Types of Estuaries -Partially mixed estuaries: these estuaries have a strong seaward flow of freshwater at the surface and a strong inflow of seawater at depth.

22 Types of Estuaries -Fjord estuary: these are deep estuaries with little tidal mixing and high river input. -At the bottom of the fjord estuary, particularly in fjords with steep sills, a stagnant saltwater layer can form.

23 So, which one is it? Fjord? Partially mixed? Well mixed? Salt-wedge?