PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Proceedings-Research on Coniferous Forest Ecosystems-A symposium.
Bellingham, Washington-March 23-24, 197 2
Dynamics of nutrient supply and
primary production in
Lake Sammamish, Washington
Eugene B . Welc h
an d
Demetrios E . Spyridakis
Department of Civil Engineering
University of Washingto n
Seattle, Washingto n
Abstract
Lake Sammamish, which lies about 12 miles east of Seattle, Washington, with moderate depth (mean 17 .7 m )
and area (19.8 km 2 ), ranks third in productivity of the four Cedar River drainage lakes and can be classified
mesotrophic. While diversion of over one-half the P from nearby Lake Washington during 1963-67 was followe d
by reduction in winter mean P content and a rapid shift from eutrophy to mesotrophy (Edmondson 1970) ,
mean winter P content and measured characteristics of plankton response have not changed in Lake Sammamis h
following a diversion of similar magnitude . Annual nutrient budgets suggest a reduction in sedimented P sinc e
diversion but little change in the quantity of P released from anaerobic sediment . P availability in the water
column (winter mean content) appears to be controlled by Fe precipitation to a greater extent than in Lak e
Washington. Experiments in situ show that N and P are equally limiting to summer phytoplankton productivity ,
but as found in Lake Washington, P may be of more long-term significance.
Introduction
The supply of limiting nutrient is probabl y
the most significant factor that determine s
the trophic status of a lake . This relationshi p
can be affected by several factors, particularl y
those that control nutrient supply such as
morphometric and hydrologic conditions .
Vollenweider (1968) has related supply of N
and P to trophic status of 20 lakes and foun d
that the relationship was dependent on lake
morphometry expressed as mean depth . This
relationship illustrates that reasonably reliable
predictions about the primary production and
trophic status of lakes are possible with in -
formation on the supply of limiting nutrient
and lake morphometry . Such predictability i s
valuable in the management of man's encroachment
on lakes. Of still more value is
knowledge of the response rate of trophi c
status indicators to changes in nutrient
supply .
This paper presents preliminary findings on
a nutrient supply budget for Lake Sammamish
near Seattle, Washington, and ho w
alteration in that supply by sewage diversio n
has affected nutrient limitation and primar y
production . The response in Lake Sammamish
to nutrient diversion is compared to that in
Lake Washington and mechanisms are hypothesized
to explain the delayed recovery in Lak e
Sammamish . Their trophic status is compare d
to that of other study lakes in the Cedar River
drainage, Findley Lake and Chester Mors e
Lake, with the ultimate intent of refining predictive
relationships among trophic status ,
nutrient supply and morphometric factors i n
lakes. Prediction of the rate of response o f
trophic status indicators to change in nutrien t
supply should also be enhanced by detaile d
comparison of manipulated Lakes Sammamish
and Washington .
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