Environmental Factors Promoting and Regulating N Fixing Blue-Green Algal Blooms in the ...

80 Pages·2007·3.3 MB·English

Environmental Factors Promoting and Regulating N Fixing
Blue-Green Algal Blooms in the Chowan River, %CI..
Hans W. Paerl
Institute of Marine Sciences
University of North Carolina
Morehead City, North Carolina 28557
The work upon which this publication is based was supported in part by
funds provided by the Office of Water Research and Technology, U. S. Depart-
ment of the Interior, Washington, D.C., through the Water Resources Research
Institute of The University of North Carolina as authorized by the Water
Research and Development Act of 1978.
Project B-127-NC (b)
Agreement No. 14-34-0001-0274

Table of Contents
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abstract ii
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgments iv
. . . . . . . . . . . . . . . . . .
Summary. Conclusions and Recommendations v
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction 1
. . . . . . . . .
Sampling and Experimentation Sites. Method. .an.d .M.at.er.ia.ls . . . . . . . . . . 3
Primary productivity measu.re.m.en.ts . . . . . . . . . . . . . . . . . . 5
N fixationmeasurements 8
2 .
Transect primary productivity .an.d .N2. f.ix.at.io.n .m.ea.sur.em.e.nts. . . . . . 1 0
0 /temperature measu.re.m.en.ts . . . . . . . . . . . . . . . . . . . . . 1 0
2
Nutrient analyses . . . . . . . . . . . . . . . . . . . . 1 1
Ammonia determinations . . . . . . . . . . . . . . . . . 1 1
Orthophosphate de.te.rm.i.na.tio.ns. . . . . . . . . . . . . . . . . . 1 2
pH measurements . . . . . . . 1 2
Humic acid estimates and concentration techniques 12
Results and Discussion . .
The integration of physical. chemical and biotic features of
the-lower C.ho.w.an .R.iv.er. . . . . . . . . . . . . . . . . . . .
ThermalRegime . . . . . . . . . . . . . . . . . . . . .
Dissolved0 patterns . . . . .
~ h o t o s ~ n t h e ~ i caacltilv~e radiation (P A. R ) irradiance and
transmittance . . . . . . . . . . . . .
Temporal patterns of ambient nutrients . . . . . . . . . . .
Salinity regimes in the lower Chowan River .
Spatial and temporal patterns of in situ primary pro.d.uc.tiv.it.y . .
Vertical distribution of primary productivity
. . . . . . . . .
Temporal patterns of primary productivity
.
Effects of reduced P.A.R. transmission on primary productivity
Chemical effects of pulp m i l l effluent discharge on primary pro-
duct ivity . . . . . . . . .
Humic acid bioassays and their interpretation
N2 fixation and bl.ue.-g.re.en. a.lg.a.l b.lo.om.s .in. t.he. l.ow.er. C.ho.wa.n . . .
River 1980
N2 fixation and bl.ue.-g.re.en. a.lg.a.l b.lo.om.s .in. t.he. l.ow.e.r C.ho.w.an . . .
River 1981
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Literaturecited 61

Abstract
In order t o identify the environmental factors promoting and sustaining
blue-green algal bloom potential in the lower Chowan River, primary produc-
tivity, N2 fixation and the physical-chemical parameters regulating these
--
processes, were examined in situ a t a location previously known t o support
blooms. A combination of parameters proved instrumental in promoting
blooms during 1980. Periods of weak thermal stratification, particularly
during warming periods, coupled with phosphorus sufficiency, were crucial
t o N fixing blue-green algal bloom development. Phosphorus sufficiency
coul8 be stablished a t relatively low ambient orthophosphate levels
(<5ppP*!L9). Indirectly, nitrogen sufficiency was important as well.
Spring diatom and green algal blooms relied heavily on nitrogenous nutrients
(nitrate and ammonia) for maximum development; the degree of spring bloom
development was related t o the potential for subsequent deoxygenation
of river sediments and overlying waters during warm, weakly stratified
summer periods. Maximum deoxygenation was usually coupled with maximum
blue-green algal bloom development.
Additional physical and chemical features proved t o be crucial factors
in altering bloom development. Pulp m i l l effluent, which was a highly
significant water mass during the drought year 1981, altered spring bloom
development. Effluent showed negative effects on photosynthetic production,
both through strong coloration of waters, thereby restricting transmission
of photosynthetically active radiation (P.A.R.), as well as chemically
inhibiting growth. The chemical inhibition affected non blue-green algal
growth more severely than blue-green algal growth. This form of inhibition
is related t o the strong metal chelating abilities of humic constituents
of effluent, inducing a trace metal deficiency which blue-green algae
could overcome. Hence, it appears that high humic loading (due t o pulp
m i l l effluent) may potentially favor blue-green algal over more desirable
diatom and green algal species, since blue-green algae can form surface
scums (alleviating restricted P,A.R. transmittance) and can counter growth
inhibition due t o humic chelation of essential trace metals.
Salinity increases, observed during the drought of 1981, were strong
deterrents t o blue-green algal bloom formation during the summer months,
even when other environmental conditions proved conducive t o blooms.
Both the reduction in effluent-inhibited spring phytoplankton growth and
absence of blue-green algal blooms in 1981 led to nearly a 3-fold reduction
in primary productivity compared t o 1980.
It should be noted that 1981 was an unusually dry year, thereby empha-
sizing the growth-altering effects of pulp m i l l effluent and elevated
salinity. In the case of pulp m i l l effluent, which is discharged during
a l l years, undesirable alteration (favoring blue-green algal growth) of
the producer level of the food chain might be expected in the long run.
Lastly, it is stressed that constraints on both nitrogenous and
phosphorus inputs be instituted. A t their current levels both nutrient
sources lead to blue-green algal blooms, either directly or indirectly.
It was shown that spring nitrogen inputs created the potential for
deoxygenation of bottom waters. These deoxygenation events lead to periodic
pulses of phosphorus release. Coupled with the fact that nitrogen require-
ments of summer blue-green algal blooms are met by N fixation, restraining
2
phosphorus loading (of sediments) on a year-round basis would be a useful
step towards alleviating bloom potential.
iii
Acknowledgments
The field and laboratory assistance of Institute of Marine Science
personnel and graduate students is highly appreciated. J. Ustach, P.
Bland, J. Blackwell, M. Haibach, K. Gallucci and J. Tucker collected many
of the field samples, aided with field experiments and provided laboratory
analyses of samples, Additional field help was provided by J. Fuquay,
S. Mackintosh, J. Winkler, R. Lamar, J. Wheeler, C. Davies and C. Coughanowr.
Particular thanks go to P. Bland, J. Garner, W. Link and P. Boyd for typing
this manuscript, preparing figures and proofreading the report.
Valuable salinity and nutrient loading data, as well as communication
of field conditions, were provided by the N.C. Department of Natural Resources
and Community Development, Division of Environmental Management
(at Raleigh and Edenton, N.C.). The exchange of research information
with Drs. E. J. Kuenzler, A, M, Witherspoon and S. Mozley proved useful
in the preparation of this report.
Lastly, we are grateful to W. Brake of Brake's Marina, Harrelsville,
N.C. for providing docking and launching facilities as well as managing
to keep our research vessel from sinking during several intense thunderstorms.

Summary, Conclusions and Recommendations
In retrospect, i f salinity had not played the important inhibitory role
that was witnessed during the summer of 1981, physical and chemical conditions
would have favored a blue-green algal bloom of a t least 1980's dimensions.
In arresting potential blooms in 1981, salinity increases should be considered
as a fortuitous event, not likely to repeat itself in a high percentage of
future years. In the long run, the excessive nutrient and pulp m i l l effluent
inputs w i l l remain the main sources of undesirable blue-green algal bloom
potential and disruption of the river's food chain. Furthermore, unlike sa-
linity fluctuations, nutrient and effluent loading are variables which can
be controlled by man, through proper management practices in the Chowan River
catchment. The appearance of blue-green algal blooms over the past 10 years
is a troubling sign of changes in the particulate matter on which grazing
and filter-feeding invertebrates must rely. An equally troubling phenomenon
is the differential inhibitory effect pulp m i l l effluent has on the phyto-
plankton community. The long-term effect could be an altered food chain,
which w i l l be dependent on the utilization of undesirable as opposed to de-
sirable phytoplankton. It is conceivable that such a food chain w i l l yield
less desirable fish and shellfish as well as carnivores. In other words,
man's activities, in terms of sports fishing, commercial fishing, and tourism
w i l l be adversely affected.
Blue-green algal blooms and nutrient loading in the lower Chowan River:
The importance of restraining both nitrogen and phosphorus inputs
In most aquatic ecosystems the appearance of blue-green algal blooms
signifies excessive nutrient loading and advanced eutrophication. Such
conditions have been well-documented in several lakes which, under the
influence of excessive nutrient loading, have experienced blue-green algal
blooms. Those include Lake Erie (Dobson e t a1.1974; Schelske and Roth 19731,
Clear Lake, California (Horne and Goldman 1972), Lake Trummen in Sweden
(Cronberg et al. 1975), Lake Washington (Edmondson 19721, Heart Lake, Canada
(Lean 1973) and several artificially enriched lakes in the Canadian Experi- .
mental Lakes Area (E. L.A. ) of Ontario, Canada (Schindler et al. 1971; 19731
In the case-of Lakes Erie, Trummen as well as the E.L.A., eutrophicating
trends and parallel dominance by blue-green algae (particularly N2-fixing
genera) were reversed by controlling nutrient, and in particular, phosphorus
inputs. In the case of N2 fixing blue-green algae, constraints on phosphorus
inputs appear to be the most effective "first step" in minimizing bloom
potential (Shindler et al. 1980; Shapiro 1978).
Despite the above documentation on the effectiveness of phosphorus
constraints in minimizing blue-green algal growth, the diverse aquatic
ecosytems experiencing blue-green algal blooms exhibit a wide range of ambient
phosphorus concentrations. An example of such diversity can be seen by com-
paring Neuse and Chowan River orthophosphate concentrations, Both rivers
are currently supporting summer blue-green algal blooms; however, the Neuse
River contains roughly 5 to 20 times the summer orthophosphate concentrations
observed in the Chowan River, Despite the high nutrient loads in the Neuse
River, the lower Chowan River has experienced more frequent widespread
blue-green algal blooms over the past 10 years. It would appear that due
to proper physical conditions (including thermal stratification during calm
weather periods, sluggish water movement), bloom periods are often quickly
initiated in the Chowan River, even in response to relatively small nutrient
enrichments. Between these rivers differential sensitivities of their waters
complicate rule-of-thumb decisions on acceptable or tolerable nutrient levels.
In the case of phosphorus, blue-green algae have developed a variety of
mechanisms which allow for sustained growth even at low ambient nutrient concen-
trations. These include: a) high enzymatic affinities for low ambient ortho-
phosphate concentrations (Rhee 1982), b) the ability t o store phosphorus intra-
cellularly for use during ambient phosphorus depletion (Kuhl 19681, c) the
capacity t o utilize organic sources of phosphorus under conditions of orthophos-
phate depletion by excreting alkaline and/or acid phosphatases capable of
clearing phosphate from organic molecules (see Wetzel 1981 for a review) and,
d) alteration of buoyancy, permitting short-term vertical movement into
phosphorus-rich bottom waters (Shindler et al. 1980).
An additional factor t o consider is the phosphorus recycling rate, or
time span between the uptake, excretion, mineralization and reutilization
of the orthophosphate pool (Lean 1973). Ambient orthophosphate pools can
often exist near the lowest level of detection for substantial periods of
time (weeks) during bloom activity. It might be assumed that phosphorus
availability would be restricted a t such times. However, given effective
recycling of phosphorus, a relatively large amount of phytoplankton biomass
can exist on a small pool of dissolved orthophosphate (Lean 1973). The
addition of even a small amount of orthophosphate could have a dramatic effect
on enhancing the size of an algal bloom if phosphorus cycling were efficient.
Elaboration on this subject w i l l be forthcoming in Dr. E. J. Kuenzlerls Chowan
River study report.
When N fixing blue-green algal genera are present i n the Chowan River
2
and climatic factors favor their dominance, we have shown that even a small
(10 ppb) increase in ambient orthophosphate w i l l help stimulate surface blooms
(Mackintosh et al. 1980; Paerl and Kellar unpublished data). Therefore pro-
cesses leading to increased phosphorus availability a t such times w i l l be
instrumental in stimulating bloom activity. Processes include a ) pulses of
orthophosphate release from sediments, particularly poorly oxygenated sedi-
ments, b) agricultural surface runoff, which can be greatly accelerated during
summer thunderstorm periods, c) release of phosphorus from septic tanks and
municipal waste treatment plants, and d) release of phosphorus from other
point sources, including industrial concerns and marinas.
Current phosphorus inputs exceed levels which w i l l initiate and sustain
nuisance blooms. To some extent river sediments have accumulated previous
yearsf nutrient input. This form of nutrient storage is susceptible to future
leaching and release during oxygen-poor periods, which can be expected i n
the immediate future, even given a few years of reduced nutrient loading,
However, if nutrient loading is reduced over a substantial period (5 to 10
years), the nutrients released from sediments w i l l steadily decrease as well.
Eventually sediments w i l l become nutrient-deficient and w i l l not be able t o
support blooms; a lack of bloom activity w i l l lead to lower potential for
deoxygenation of sediments known t o be responsible for pulses of released
orthophosphate.
A period of reduced nutrient loading coupled with continued nutrient