Marine Ecosystems

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Contents

Introduction

A marine ecosystem is a natural saltwater-based unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the non-living physical (abiotic) factors of the environment. Our study site in Southeast Alaska consists of spatially dense aggregations of glaciers with boreal and marine ecosystems.



Eran Hood has recently started looking into the connection between partially glaciated watersheds and marine ecosystem nutrient flux. This page describes some of these ideas.


A technology aside: This link connects to a resource for coastal web atlases.


View of Mendenhall Glacier (distance) and fog above the Mendenhall River plume

Water chemistry

Sea water salinity is measured in parts per thousand, where the open ocean is pretty salty at 35 ppt, roughly, and most of that is from sodium and chlorine ions. Salinity in combination with temperature determines the density of sea water which varies from one location to another, both laterally in the map sense and vertically through the water column.


We are interested in the fresh water plumes from rivers as they pour out into the ocean, particularly in coastal Southeast Alaska. Here we can estimate there is roughly one watershed for every mile or two of coastline, meaning that this region consists of many thousands of such watersheds. Many are ice covered to some extent, where glaciers play a major role in determining the chemical and biological composition of this freshwater input to the marine environment.


Because the fresh water has less density than salt it tends to flow out across the surface of the ocean forming a thin fresh-water lens. For example at Fritz Cove off the north end of Douglas Island about 4 km from the mouth of the Mendenhall River we placed a sensor just below the surface. The readout is shown below where the first number is water temperature in degrees Celsius and the third number is salinity in parts per thousand. The bottom number is pH.


Just below the surface the water is fresh (and cold)


Again: Ocean water would be about 35 ppt and our body chemistry runs at about 0.9 ppt; so this water at 0.77 ppt is practically drinkable. (I tried some and it was just a little salty.)


Now we push the probe down about 2 meters below the surface in the same spot and we get these values on the probe:


Two meters down the water is salty and a little warmer


This water is warmer, about twenty times saltier, and slightly more acidic; so there's your fresh water lens on the top.


How does this water mix? With tidal currents or a wind kicking up choppy seas we'd have mechanical mixing, but on a calm day with very little wave action we can imagine that salt and fresh water could remain stratified in this way for quite awhile. In this case whatever is in the fresh water might be distributed regionally in one way, whereas mixing will distribute that stuff--and here we care about nutrients like Carbon, Nitrogen and Phosphorous--in a completely different way.



Notes

Dissolved Organic Material

Lability

In chemistry a simple working definition of labile is "subject to change" or unstable.


Anthropogenic Factors

The following really should go in a humans-and-environment type section.


EDTA

A multi-dentate ligand (atom, ion, or molecule that bonds to a metal), more specifically an 'industrial' (non-biological) amino acid used for chelating (metal sequestration) applications; so commonly used that it has become ubiquitous in many water supplies:


From the Wikipedia article on EDTA:

Widespread use of EDTA and its slow removal under many environmental conditions has led to its status as the most abundant anthropogenic compound in many European surface waters. River concentrations in Europe are reported as 10-100 μg/L, and lake concentrations are in the 1-10 μg/L range. EDTA concentrations in U.S. groundwater receiving wastewater effluent discharge have been reported at 1-72 μg/L, and EDTA was found to be an effective tracer for effluent, with higher concentrations of EDTA corresponding to a greater percentage of reclaimed water in drinking water production wells.
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