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Detecting impacts and setting restoration targets in arid-zone rivers: Aquatic micro-invertebrate responses to reduced floodplain inundation

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Summary 1. Water extraction from arid-zone rivers increases the time between floods across their floodplain wetlands. Less frequent flooding in Australian arid-zone rivers has impaired waterbird and fish breeding, killed riparian vegetation and diminished invertebrate and mac- rophyte communities. Restoration currently focuses on reinstating floods to rejuvenate floodplain wetlands, yet indicators to measure the success of this are poorly developed. 2. We explored the application of criteria for ecologically successful river restoration to potential restoration of floodplain wetlands on the Darling River, arid-zone Australia. Using emergence of micro-invertebrates from resting eggs as an indicator, we compared responses of taxa richness, densities and community composition in floodplain lakes with different inundation histories. 3. Increased drying of floodplain lakes reduced the number of micro-invertebrate taxa. Several key taxa were absent and faunal densities (particularly cladocerans) were reduced when the duration of drying increased from 6 to 20 years. 4. A conceptual model of the ecological mechanisms by which restoration of flooding regime could achieve the target of preserving micro-invertebrate community resilience predicts that reducing the dry period between floods will minimize losses of viable resting eggs. Protection of this 'egg bank' permits a boom in micro-invertebrates after flooding, promoting successful recruitment by native fish and waterbirds. 5. Synthesis and applications . In arid-zone rivers, micro-invertebrate densities and community composition are useful indicators of the impact of reduced flooding as a result of water extraction. Critical to successful native fish recruitment as their first feed and as prey for waterbirds, micro-invertebrates are a potential early indicator of responses by higher trophic levels. Taxon richness, density and key taxa present after flooding, all indicators of resilience, can be incorporated into targets for arid-zone river restoration. For example, one restoration target may be microcrustacean densities between 100 and 1000 L − 1 within 2-3 weeks after spring flooding. These criteria can be applied to measure the ecological success of restoration projects seeking to recover natural flood regimes. Given the high economic cost of water in arid zones, convincing demonstrations of the ecological success of environmental water allocations are crucial.
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Journal of Applied
Ecology
2007
44
, 823–832
© 2007 The Authors.
Journal compilation
© 2007 British
Ecological Society
Blackwell Publishing Ltd
Detecting impacts and setting restoration targets in
arid-zone rivers: aquatic micro-invertebrate responses
to reduced floodplain inundation
K. M. JENKINS and A. J. BOULTON
Ecosystem Management, University of New England, Armidale, NSW, 2351, Australia
Summary
1.
Water extraction from arid-zone rivers increases the time between floods across their
floodplain wetlands. Less frequent flooding in Australian arid-zone rivers has impaired
waterbird and fish breeding, killed riparian vegetation and diminished invertebrate and mac-
rophyte communities. Restoration currently focuses on reinstating floods to rejuvenate
floodplain wetlands, yet indicators to measure the success of this are poorly developed.
2.
We explored the application of criteria for ecologically successful river restoration to
potential restoration of floodplain wetlands on the Darling River, arid-zone Australia.
Using emergence of micro-invertebrates from resting eggs as an indicator, we compared
responses of taxa richness, densities and community composition in floodplain lakes
with different inundation histories.
3.
Increased drying of floodplain lakes reduced the number of micro-invertebrate taxa.
Several key taxa were absent and faunal densities (particularly cladocerans) were
reduced when the duration of drying increased from 6 to 20 years.
4.
A conceptual model of the ecological mechanisms by which restoration of flooding
regime could achieve the target of preserving micro-invertebrate community resilience
predicts that reducing the dry period between floods will minimize losses of viable
resting eggs. Protection of this ‘egg bank’ permits a boom in micro-invertebrates after
flooding, promoting successful recruitment by native fish and waterbirds.
5.
Synthesis and applications
. In arid-zone rivers, micro-invertebrate densities and
community composition are useful indicators of the impact of reduced flooding as a
result of water extraction. Critical to successful native fish recruitment as their first feed
and as prey for waterbirds, micro-invertebrates are a potential early indicator of
responses by higher trophic levels. Taxon richness, density and key taxa present after
flooding, all indicators of resilience, can be incorporated into targets for arid-zone river
restoration. For example, one restoration target may be microcrustacean densities
between 100 and 1000 L
1
within 23 weeks after spring flooding. These criteria can be
applied to measure the ecological success of restoration projects seeking to recover
natural flood regimes. Given the high economic cost of water in arid zones, convincing
demonstrations of the ecological success of environmental water allocations are crucial.
Key-words
: cladocerans, dryland river, environmental water allocation, irrigation impacts,
micro-invertebrates, resilience, river restoration
Journal of Applied Ecology
(2007)
44
, 823–832
doi: 10.1111/j.1365-2664.2007.01298.x
Introduction
Many Australian floodplain wetlands suffer severe
degradation as a result of flow regulation for town
supply and irrigation (Kingsford 2000; Lemly, Kings-
ford & Thompson 2000; Kingsford, Jenkins & Porter
2004). Regulation reduces flooding to some floodplain
wetlands (because of extraction) while permanently
flooding or reducing flow variability to others (because
of delivery). Current river restoration projects are
returning water to parched floodplain wetlands via
legislated environmental water allocations and the
Correspondence: K. M. Jenkins, Ecosystem Management,
University of New England, Armidale, NSW, 2351, Australia
(fax +61 2 67732769; e-mail kjenkin6@une.edu.au).
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A. J. Boulton
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,
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purchase of water licenses (Jenkins, Boulton & Ryder
2005). With insufficient water to recover natural flood
patterns, the challenge is to predict thresholds for flood
frequency, duration and timing that will restore structure,
function and resilience (Lake 2000) to arid-zone
floodplain wetlands. Setting ecologically meaningful
targets and indicators to assess ecological responses to
restoration (Lake 2001; Jansson
et al
. 2005; Palmer
et al
. 2005) is a controversial emerging area of research
(Middleton 2003; Boedeltje
et al
. 2004; Kingsford &
Auld 2005; Rood
et al
. 2005; Sheldon 2005).
Almost half the world’s land area lies in the arid
zone, characterized by low and variable rainfall (Comín
& Williams 1994; Thoms, Beyer & Rogers 2006) yet
supporting extensive arid-zone wetlands and rivers
that drain or flow through these dry regions (defined in
Boulton 2000). In the largely arid Murray–Darling
Basin, Australia, 24 700 wetlands larger than 1 ha
cover 6306 000 ha (Kingsford, Curtin & Porter 1999).
Although many of these wetlands connect to rivers
during floods, flood frequency has been reduced by
20–81% as a result of water resource developments,
and the length of time that floodplain wetlands remain
dry is increasing (Kingsford 2000; Jackson
et al
. 2001;
Thoms, Beyer & Rogers 2006). For example, the
Macquarie Marshes, a 200 000-ha Australian Ramsar
floodplain wetland that flooded naturally every 1–2
years, has not had a significant flood for 6 years (Jenkins,
Boulton & Ryder 2005) and has reduced in size by 50%
(Kingsford & Thomas 1995). Irrigation has dried out
many other significant floodplain wetlands, including
the California and Nevada wetlands in North America,
the Aral Sea in central Asia, the Senegal Delta and
Hadejia-Nguru wetlands in Africa, and the Doñana
wetland in southern Spain (Lemly, Kingsford &
Thompson 2000; Tockner & Stanford 2002).
In pristine arid-zone rivers, inundated floodplains
teem with life as micro-invertebrates and insects
colonize the turbid waters (Maher & Carpenter 1984;
Shiel
et al
. 2006), autotrophic communities and meta-
bolism boom (Costelloe
et al
. 2005; Bunn
et al
. 2006),
waterbirds congregate in their thousands (Kingsford,
Curtin & Porter 1999), fish populations proliferate
(Puckridge
et al
. 1998) and aquatic macrophytes
germinate (Capon & Brock 2006). Micro-invertebrates
(> 35
µ
m) hatching from sediments or imported from
the river (Jenkins & Boulton 2003) comprise a signifi-
cant proportion of the biomass (Crome & Carpenter
1988) and play a critical role in food webs (Boon &
Shiel 1990). They are vital to the successful recruitment
of Australian native fish, including golden perch
Macquaria ambigua
, silver perch
Bidyanus bidyanus
and Murray cod
Maccullochella peelii
, which depend
on them for their first feed after hatching (Culver &
Geddes 1993; King 2005). Pulses in native fish density
after flooding in arid-zone rivers are linked to micro-
invertebrates as a key dietary resource (Gehrke
et al
.
1995; Puckridge
et al
. 1998; Balcombe
et al
. 2005). Many
waterbirds, such as pink-eared ducks
Malacorhynchus
membranasceus
, Australasian shoveler
Anas rhynchoti
and freckled ducks
Stictonetta naevosa
feed primarily
on micro-invertebrates (Crome 1985). The numbers of
pink-eared ducks rose and fell with micro-invertebrate
densities in Lake Merimajeel in inland Australia (Crome
1985), while tens of thousands of filter-feeding waterbirds
were recorded in the Cooper system after floods (Kings-
ford, Curtin & Porter 1999). Predatory macro-invertebrates
eat micro-invertebrates (Boulton, Sheldon & Jenkins
2006) that, in turn, feed on algae, bacteria, fungi and
protozoans, indirectly affecting nutrient cycles and fluxes
of carbon mediated by bacteria (Boon & Shiel 1990).
However, drying is unavoidable: habitats contract
and fragment as a result of water loss, prompting resistant
strategies (retreats to refugia, diapause) and death
because of stranding and desiccation (Stanley, Fisher
& Grimm 1997). Targets and indicators for arid-zone
river restoration must incorporate this variability and
ability to recover after flooding that typifies the ‘boom–
bust’ ecology of arid-zone rivers and avoid interpreting
‘bust’ populations as ‘unhealthy’ (Sheldon 2005).
Although native biota in arid-zone rivers are extremely
resilient, responding rapidly to flooding despite years
without water (Kingsford, Curtin & Porter 1999; Jenkins
& Boulton 2003), the ecosystem processes and resilience
of algae, invertebrates, vegetation, fish and waterbirds
are adversely affected by loss of floods (Boulton &
Lloyd 1992; Ellis, Crawford & Molles 1998; Kingsford
& Johnson 1998; Dahm
et al
. 2003; Valett
et al
. 2005).
Depressed pulses of micro-invertebrates with increased
duration of drying deprive fish, filter-feeding water-
birds and macro-invertebrates of a vital food supply
and, as such, may be good early warning indicators of
impending impacts in arid-zone floodplain wetlands.
This study investigated the association of emergence
of micro-invertebrates from resistant resting stages
with time since flooding. Does their resilience, as indi-
cated by the response of taxon richness and density to
flooding after dry periods, diminish with increased time
since flooding? If drought-resistant micro-invertebrate
resting stages are depleted because of a lack of flooding,
we hypothesized that communities from lakes last flooded
20 years ago would have fewer taxa and lower densities
than those from lakes last flooded 6 years ago. With
these data, we wished to assess the potential application
of criteria for ecologically successful river restoration
(Jansson
et al
. 2005; Palmer
et al
. 2005) to the restoration
of arid-zone floodplain wetlands via increased flooding.
Methods
study sites and flood history
Teryaweynya Lakes comprise an ephemeral floodplain
lake system associated with 150 km of floodplains and
channels on the lower reaches of the 2740-km Darling
River in south-western New South Wales, Australia
(see Fig. S1, Supplementary material). Sixty per cent of
the 650 000 km
2
catchment is semi-arid or arid (Thoms
825
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restoration
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& Sheldon 2000). Inundation of these lakes relies on
floods in the Darling River of long duration (> 30 days) at
heights above 8·5 m, or 25 000 ML day
1
at Wilcannia.
Records (18902000) indicate flood frequencies for
individual lakes ranging from 1 in 10 to 1 in 50 years.
Although there are historical records available for
flows of the Darling River, there are no gauge records
for flows to individual lakes. Fortunately, many land-
holders have kept diaries of flood events for the creeks,
anabranches and lakes of the lower Darling River
dating back to the late 1800s. We compiled flood history
records from a report by a local historian (Withers
1996) and interviews with local landholders. Lakes
were clustered into four groups based on time since the
last flood pulse: 6, 20, 50 and 106 years. We selected
lakes that last flooded relatively recently (6 and
20 years) because we wanted to relate our findings to
the hydrological effects of river regulation that are
increasing the time between medium-sized floods from
6 (4 – 8) towards 20 (10 – 20) years (Thoms & Sheldon 2000).
Three lakes that last flooded 6 years (Pelican Lake,
Dead End Lake and an unnamed lake hereafter referred
to as Little Victoria Lake) and 20 years ago [Brick Kiln
Lake, Albemarle 1 (unnamed) Lake and Brennans Lake]
were selected to maximize interspersion across a broad
geographical region. Although care was taken to exclude
lakes known to have flooded from rain events in the last
20 years, it was later discovered that Brick Kiln Lake
had flooded briefly from rainfall in 1990. The sampled
lakes ranged from 60 to 433 ha and up to 3 m deep. The
prevailing wind was to the north-east, evidenced by land-
holder records and geomorphology of lake dunes.
sampling design
A hierarchical sampling design was used to investigate
the effects of flood history (FH) and wind direction
(WD) on the response of micro-invertebrates to flooding
(see Fig. S1 in the supplementary material). Lakes
(LK) were nested within flood history. Repeated
measures were carried out on subjects (samples) on days
1, 3, 7, 10, 14, 21 and 28 after flooding (flood day, FD)
(see below). The FH factor included two levels, with
three lakes last flooded 6 years previously and three
lakes that last flooded 20 years previously. Within each
lake there were two sites, upwind and downwind, in
case adult and resting stages were blown preferentially
during drying. WD and FD were fixed factors and
lakes were a random factor. Sites were located at
similar altitudes towards the edge of lakes. Within each
20
×
20-m site, five samples were collected randomly
(see Fig. S1 in the supplementary material).
sediment collection and inundation
Lake sediments were collected in March and April
1996 using methods described in Jenkins & Boulton
(2003). Overlying detritus and vegetation were included
in the samples. Sampling points that fell directly on
perennial vegetation (e.g. spiny lignum
Muehlenbeckia
horrida
) were moved left 1 m. Sediments to 10 mm
depth were placed carefully in plastic microcosms
(165
×
165
×
115 mm) for transport to a glasshouse.
Samples were flooded in a glasshouse from June–
September 1996 to coincide with winter–spring flooding
in the lower reaches of the Darling River. They were
flooded in five blocks of 12 samples, with one sample
from each treatment and lake (2 WD
×
2 FH
×
3 LK)
included in each block. All treatments and blocks were
randomly assigned positions in the glasshouse. Flooding
was simulated using deionized water (1936 mL) because
it was not logistically possible to inundate samples with
floodwater from lakes 1500 km away. Water quality
was measured in one randomly selected microcosm
from each treatment replicate (2 WD
×
2 FH
×
3 LK)
on flood days 1, 7 and 28. Water samples (100 mL) were
collected in acid-washed polyethylene bottles, filtered
(GF-F Whatman glass fibre filters, 0·7
µ
m) and fro-
zen before analysis of soluble reactive phosphorus
(SRP) (Murphy & Riley 1962), dissolved oxides of
nitrogen (NOx-N) (Wood, Armstrong & Richardson
1967) and conductivity. Water temperature was
measured in each treatment twice daily throughout the
experimental period. On days 1, 3, 7, 10, 14, 21 and 28,
all samples were poured though a 56-
µ
m mesh, and
invertebrates were live counted under a microscope and
returned to their microcosms. Full details of processing
are described in Jenkins & Boulton (2003).
data analysis
All data were analysed by repeated-measures analyses
of variance (
anova
; see Table S1 in the supplementary
material). Residuals were examined to check for hetero-
geneous variances and non-normality (Quinn & Keough
2002). Log
10
(
x
+ 1) transformations were applied when
necessary to homogenize variances. Dependent variables
included taxonomic richness and densities of rotifers
and cladocerans. All
anova
s were carried out using
systat
for Windows, version 9·0 (
systat
Incorporated, Evanston,
IL). Tukey’s tests were employed for multiple compari-
sons where significant differences among transformed
means were detected. Equations for the explained
variance of each term in the
anova
model were deter-
mined from estimated mean squares (see Table S1 in
the supplementary material) (Quinn & Keough 2002).
Data were classified using
twinspan
(two-way
indicator species analysis; Hill, Bunce & Shaw 1975) to
identify assemblages characteristic of flood history.
Analysis was done using all 98 taxa recorded in the
samples. Of the 420 samples, 16 empty samples were
excluded. To complement the
twinspan
, community
compositions were also compared using non-metric
multidimensional scaling (NMDS) computed with
primer
(Clarke & Warwick 2001) on a Bray–Curtis
similarity matrix of fourth-root transformed data.
Composite samples of the abundances for each taxon
from five samples in upwind and downwind sites were
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analysed, reducing the data set to 42 samples (2 flood
histories
×
3 lakes
×
7 flood days). Coordinates of each
composite sample in a lake were plotted in chronological
order, generating succession trajectories (cf. Boulton &
Lake 1992) to assess change in community composition
over time. The taxa that characterized each flood history
treatment in each lake were identified using SIMPER
(similarity percentages; Clarke & Warwick 2001).
Results
water quality
Within 1 day of re-wetting, concentrations of NOx-N
and SRP increased in samples from lakes that last
flooded 6 compared with 20 years ago (Fig. 1).
Conductivity increased in both flood histories from
day 1 to 28, and was greater in lakes that had been dry
for 6 years (Fig. 1). Dissolved oxygen also increased,
generally reaching saturation by day 14. Water temper-
atures varied from 9 to 20
°
C, comparable with those
recorded in lakes (12·5–19·2
°
C) near the study area
(Jenkins & Boulton 2003).
taxon richness
Invertebrate taxon richness varied dramatically between
lakes with different flood histories. In lakes dry for
6 years, 38 taxa were detected, 12 more than in lakes
dry for 20 years. Eighteen taxa were unique to lakes
dry for 6 years. Although eight of these occurred in
fewer than five samples, several common taxa (the
rotifers
Asplanchna
,
Polyarthra
,
Filinia
and
Conochilus
and calanoid copepods) were absent in lakes dry for
20 years. The six taxa that only occurred in the lakes
dry for 20 years were from one sample and were all
rotifers.
Significantly higher numbers of taxa emerged from
lakes flooded 6 compared with 20 years previously,
accounting for 23·5% of the variation (
P
< 0·001; Fig. 2)
(term 1; Table 1). Taxon richness varied significantly
over flood day (10·5% variation, term 7; Table 1), with
fewer taxa on day 1 compared with days 7 (Tukey’s
P
= 0·005) and 1028 (Tukey’s
P
< 0·001). Numbers of
taxa on day 3 were lower than those on all other flood
days (
P
< 0·006) except day 7. Taxon richness increased
sharply over time in the lakes last flooded 6 years ago
(Fig. 2).
The greatest variance in taxon richness, for all flood
days combined, occurred in the interaction between
Fig. 1. Changes in nitrate (a), soluble reactive phosphate (b)
and conductivity (c) over time since flooding. Data are means
and SE from the six sites from lakes flooded 6 years
(unshaded) and 20 years ago (shaded).
Fig. 2. Mean + SE (n = 5) number of taxa per microcosm
over time since flooding in lakes last flooded 6 years (left,
unshaded) and 20 years ago (right, shaded). Downwind sites
(circles) and upwind sites (triangles) are shown.
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lakes within flood history and wind direction (52·4%,
term 5; Table 1). This reflected the low numbers of taxa
in the downwind sites in Dead End Lake and Albemarle
1 Lake, reversing the trends seen in the other two lakes
flooded 6 and 20 years ago (Fig. 2). Both the downwind
sites with few taxa had low dissolved oxygen because of
decaying vegetation in the samples.
taxon density
Densities of rotifers increased more steeply over time in
samples from lakes flooded 6 compared with 20 years
ago (term 8; Table 1 and Fig. 3). Flood history
accounted for 20·4% of variation in the model, but the
similar densities on day 28 coupled with high variation
among samples (39·0%) and lakes (10·1%) contributed
to the non-significant test of flood history (terms 1, 2
and 6; Table 1). Rotifer densities differed among lakes
within flood history (term 2; Table 1 and Fig. 3) because
of higher densities in Brick Kiln Lake compared with
the other two lakes (Fig. 3). The significant interaction
between lakes within flood history and wind direction
(term 5; Table 1) reflected reduced densities in the
downwind site in Dead End Lake (Fig. 3) and the
higher densities in the downwind site in Brick Kiln
Lake (Fig. 3). Rotifer densities showed significant
temporal variation (term 7; Table 1 and Fig. 3), with
lower densities on day 1 than days 14, 21 and 28 (Tukey’s
P
= 0·010, 0·001 and < 0·001, respectively).
Cladocerans were either absent or rare in lakes flooded
20 years previously, whereas they were detected in all
sites from the recently flooded lakes, reaching densities
of 1000 m
2
in most sites by day 21 (terms 1 and 5;
Table 1 and Fig. 4). Again, densities were higher in
downwind sites, except in Dead End Lake where
cladocerans were not detected until day 21, and then
only in low numbers (term 5; Table 1 and Fig. 4).
Temporal variation in cladoceran densities was significant
(term 7; Table 1). Cladocerans did not occur in samples
until day 7, when their densities were 10 m
2
, significantly
lower than on days 10 (Tukey’s
P
= 0·017) and days 14 –28
Table 1. anova results for untransformed taxa richness and log
10
(x + 1) transformed densities of rotifers and cladocerans.
Significant P-values (< 0·05) are shown in bold and variance components are indicated (%VC)
Source of variation
Taxonomic richness Rotifers Cladocerans
MS FP%VC MS FP%VC MS FP%VC
Between samples
1 Flood history, FH 406·117 102·505 0·001 23·5 94·155 5·344 0·082 20·4 24·175 7·247 0·055 17·3
2 Lakes within FH, L(FH) 3·962 0·287 0·885 0 17·618 3·528 0·013 10·1 3·336 1·875 0·130 3·9
3 Wind direction, WD 0·688 0·004 0·951 0 1·711 0·072 0·801 0 4·700 0·543 0·502 0
4 FH × WD 0·402 0·002 0·963 0 6·163 0·261 0·636 0 5·163 0·596 0·483 0
5 L(FH) × WD 163·352 11·824 0·000 52·4 23·615 4·729 0·003 29·7 8·661 4·868 0·002 34·4
6 Samples (residual) 13·815 24·2 4·994 39·9 1·779 44·4
Within samples
7 Flood day, FD 46·208 16·064 0·000 10·5 20·414 9·086 0·000 11·9 12·027 22·536 0·000 20·5
8 FD × FH 33·956 11·070 0·000 15·1 10·956 4·876 0·002 11·4 2·373 4·446 0·004 6·6
9 FD × L(FH) 3·067 1·288 0·170 1·0 2·247 1·936 0·006 4·3 0·534 1·436 0·089 1·7
10 FD × WD 1·238 0·115 0·994 0 2·933 1·420 0·248 0 0·483 0·454 0·835 0
11 FD × FH × WD 3·947 0·326 0·917 0 1·828 0·885 0·521 0 1·133 1·066 0·410 0·5
12 FD × L(FH) × WD 10·741 4·509 0·000 24·5 2·066 1·780 0·015 7·1 1·063 2·861 0·000 14·8
13 Samples × FD (residual) 2·382 48·9 1·160 64·0 0·372 55·8
Fig. 3. Mean + SE (n = 5) density of rotifers per m
2
observed
after inundation. Graph details follow Fig. 2.
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(P < 0·001) (Fig. 4). Trends in cladoceran densities
over time were not consistent between flood history
(term 8; Table 1) as densities did not increase in lakes
dry for 20 years (Fig. 4).
community composition
twinspan classification of the sample data indicated
striking changes in community structure over time and
between flood history treatments (Fig. 5). Flood days
1–3 from both flood histories, along with flood days
7–28 from lakes last flooded 20 years ago (A–D), were
separated in the first division from flood days 728 in
the more recently flooded lakes (E–G; Fig. 5). Only
seven of the 101 samples in the latter group were from
lakes last flooded 20 years ago. Groups E–G were
characterized by a diversity of rotifers (Cephalodella
spp., Polyarthra, Brachionus spp., Filinia, Asplanchna,
Conochilus) and crustaceans (Macrothricidae, Chydoridae,
Daphniidae, calanoid copepods). Groups A–D separated
on the second division into early flood days 1–3 (A
and B) and later flood days 728 from lakes last
flooded 20 years ago (C and D) (Fig. 5). The early
flood days were characterized by one protozoan
taxon, nematodes and a bdelloid rotifer, while the later
flood days were characterized by diverse protozoans,
Volvox sp. and, in some samples, low numbers of
cladocerans.
Community structure in lakes flooded 6 and 20 years
previously was similar 1 day after re-wetting because of
seven shared protozoan taxa (Fig. 6). However, 1 month
after flooding, the community composition between
flood histories diverged (Fig. 6) because of a suite of
rotifers (Cephalodella catellina, Brachionus bidentatus,
Asplanchna sieboldi, Polyarthra dolichoptera and several
bdelloids) and crustaceans (Daphniidae, Macrothricidae,
assorted nauplii, Chydoridae and ostracods) charac-
terizing lakes flooded 6 years ago compared with the
predominance of protozoans and nematodes in lakes
flooded 20 years ago.
Fig. 4. Mean + SE (n = 5) density of cladocerans per m
2
observed after inundation. Graph details follow Fig. 2.
Fig. 5. twinspan dendrogram of 404 samples (flood history, wind, lakes) over time since flooding.
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Discussion
The spectacular pulses in densities of invertebrates, fish
and waterbirds after floods in arid-zone rivers (Kingsford,
Curtin & Porter 1999; Jenkins & Boulton 2003) rely on
maintenance of resistant populations, either in aquatic
refugia or as dormant life stages (Stanley, Fisher & Grimm
1997). Given the importance of micro-invertebrates in
the inundated floodplain food webs (see the Introduc-
tion), it is clear that restoration efforts must maintain these
resistant stages. Depletion of viable micro-invertebrate
dormant stages through water extraction and increased
duration of drying in arid-zone rivers may break the
links between micro-invertebrates and their dependent
fauna.
Our results show that, as periods of connectivity
between floodplain and regulated rivers become less
frequent, resistant micro-invertebrates decline and
their resilience after floods is reduced. In this study,
cladoceran production fell by more than an order of
magnitude as the duration of drying increased from
6 to 20 years. As cladocerans are the preferred prey
for many Australian native fish at their first feed and
for filter-feeding waterbirds, reduced emergence has
important ramifications for the management of native
fisheries and waterbirds.
As the duration of the dry period increases, losses of
resting eggs inevitably occur as their finite energy
reserves are exhausted (Carvalho & Wolf 1989), and
they are decomposed by micro-organisms (Moritz
1987) or eaten by predators (De Stasio 1989). Floodplain
sediments, where nutrients, seeds and eggs are stored
during dry periods, experience high summer tempera-
tures, aeolian transport, water loss, altered terrestrial
inputs and breakdown and consumption of organic
material. Changes in floodplain sediment storage during
increasing dry periods alters ecosystem processes (Ellis,
Crawford & Molles 1998; Molles et al. 1998; Dahm
et al. 2003; Valett et al. 2005) that, in turn, may also
influence the response of animal and plant populations
when flooding eventually occurs (Capon & Brock
2006). For example, the reduced pulse of nutrients in
lakes dry for 20 years may trigger lower emergence
rates, as has been shown for high salinity levels (Brown
& Carpelan 1971). Increased accumulation of organic
matter associated with reduced flooding in some
arid-zone rivers elevated respiration rates during short
(4-week) experimental floods (Valett et al. 2005),
severely depleting dissolved oxygen levels and poten-
tially inhibiting the emergence of micro-invertebrates
(Dana et al. 1988). It is likely that, during dry periods,
resting eggs accumulate downwind (lakes dry for 6 years)
but that, as the dry period increases, aeolian sediment
progressively buries resting eggs, depriving them of
suitable hatching cues (Hairston et al. 1995; Gleason
et al. 2003).
There is also evidence that cladoceran and copepod
eggs can take longer to hatch when diapause is extended
(Moritz 1987; Elgmork 1996). If there is a ‘delayed
boom’ in cladoceran numbers after a flood pulse in
lakes that have not flooded for extended periods (15
50 years), then native fish and waterbirds that breed
early may miss the peak in prey availability. In arid-zone
rivers, the timing of responses is probably critical to
successful recruitment by birds and fish because the
inundated ‘window of opportunity’ is so short.
Although our findings are from microcosm experi-
ments, the densities observed in our microcosms (143
2270 L
1
or 1000–100 000 m
2
) were within the range
recorded in temperate ephemeral ponds (675–107 000 m
2
;
Wyngaard, Taylor & Mahoney 1991) and in flooded
lakes in the study area (100–1000 L
1
; Jenkins & Boulton
2003) and nearby wetlands (50–600 L
1
; Crome &
Carpenter 1988). Further, taxon richness and community
succession trajectories converged after flooding in micro-
cosms and lakes (Jenkins & Boulton 2003), supporting
the realism of this approach, at least in the short term.
Reductions in micro-invertebrate production and
biodiversity have global implications for the restoration
of floodplain wetlands and conservation of fish and
waterbirds. For example, by 1994 more than 60% of the
annual flow in the lower reaches of the Barwon–Darling
River was being diverted for irrigation (Thoms, Beyer
& Rogers 2006), dramatically reducing flooding to
floodplain lakes on Teryaweynya Creek, the Darling
River and anabranches. In North America, 90% of the
total discharge from rivers is impacted by dams, reser-
voirs, interbasin transfers and irrigation (Jackson et al.
2001), and some 54% of wetlands has been lost (Spiers
1999; Lemly, Kingsford & Thompson 2000). In Europe,
wetland losses exceed 5065% in many countries and
up to 95% for floodplain wetlands (Spiers 1999; Tockner
& Stanford 2002). Similarly, in Asia wetland loss is
severe, with 85% of the 734 sites in the Asian wetland
directory under threat and the complete loss of signi-
ficant wetlands, such as the Red River delta floodplains
in Vietnam that covered 1·75 million ha (Spiers 1999).
Clearly, the extent of anthropogenically ‘parched’
wetlands (Jenkins, Boulton & Ryder 2005) is increasing
world-wide. However, reinstatement of increased flood
Fig. 6. NMDS showing change in community composition
for time trajectories from day 1 (D1) to day 28 (D28) for
composite samples from three lakes last flooded 6 years ago
(unshaded) and three last flooded 20 years ago (shaded).
830
K. M. Jenkins &.
A. J. Boulton
© 2007 The Authors.
Journal compilation
© 2007 British
Ecological Society,
Journal of Applied
Ecology, 44,
823–832
frequency of wetlands disconnected from arid-zone
rivers could reverse these trends. As long as regional
extinction has not occurred, restoring the natural flood
regime should recover the balance between build up
vs. loss phases of the egg bank. With prolonged inunda-
tion or serial flooding (Puckridge et al. 1998), recovery
from low numbers of long-lived resting stages may
result because of the short generation time and high
reproductive capacity of micro-invertebrates (Wyngaard,
Taylor & Mahoney 1991). To guide restoration, we have
extended a model of processes affecting egg banks (De
Stasio 1989; Hairston et al. 1995) to include effects of
the duration of drying in arid-zone wetlands (Fig. 7).
This guiding image (criterion 1; Palmer et al. 2005), of
a healthy, dynamic arid-zone floodplain wetland, must
include recruitment pulses in native fish and waterbirds
underpinned by booms in micro-invertebrates, algae,
macro-invertebrates and functioning ecosystem processes,
as well as bust periods when densities are naturally
reduced. By assessing densities of the highly responsive
lower trophic levels, we obtain a sensitive indicator of
the ecological success of restoration (Palmer et al.
2005) along with its mechanism (Fig. 7; criterion 6 in
Jansson et al. 2005).
A density of 100–1000 cladocerans L
1
within 3 weeks
of floodplain inundation (Jenkins & Boulton 2003) in
spring/summer would meet prey requirements for
larval fish (King 2004) and is a measurable improvement
in ecological condition (criterion 2; Palmer et al. 2005).
This criterion is readily assessed by examination of the
viability of the egg bank and production of cladocerans
in flooded wetlands (Hairston et al. 1995; Jenkins &
Boulton 2003; Gleason et al. 2004; Angeler & Garcia
2005). The third criterion, of achieving a more ‘self-
sustaining’ system (Palmer et al. 2005), can be assessed
by coupling the indicators in criterion 2 with a measure
of the extent of floodplain wetland inundation so that
restoration of micro-invertebrate responses occurs
over an area that matches the restoration targets for
fish and waterbird recruitment. Sustainability might
also be presumed if egg bank inputs and losses were
equivalent across inundation and drying events.
In a natural arid-zone wetland, floods alternately
disrupt aquatic and terrestrial communities, but this is
not deemed to cause lasting harm (criterion 4; Palmer
et al. 2005) because it is part of the system’s boom and
bust ecology (Sheldon 2005). In regulated systems,
shifts in species composition and accumulation of
organic material on increasingly dry floodplains can
magnify harmful effects after floods, such as black
water events with low oxygen levels or toxic leachates in
the short term (Molles et al. 1998; Valett et al. 2005),
which may lower emergence rates and kill or repel fish
(Gehrke 1991). Using floods as a restoration technique
will require research on longer term responses of newly
reconnected floodplains to predict responses of ecosystem
processes and populations and avoid irreparable harm.
Micro-invertebrates respond to changed water regimes
in floodplain wetlands and are useful indicators for
pre- and post-assessment (criterion 5; Palmer et al.
2005). Using microcosms, emergence from egg banks
can be assessed before and after restoration floods,
taking care to replicate at the scale of the process and
to address variability across relevant scales. More
importantly, we must exploit opportunities to assess
restoration success during flood events.
A conceptual model of the ecological mechanisms
by which restoration of flooding frequency will produce
a ‘self-sustaining’ viable egg bank that generates
booms of micro-invertebrates after floods (Fig. 7)
helps to illustrate the importance of restoring natural
flooding regimes. For most Australian arid-zone flood-
plain rivers, we recommend that the duration of drying
should not extend beyond 1020 years, as this appears
to be an important threshold for micro-invertebrates.
Floods every 23 years will produce rich communities,
matching requirements for aquatic vertebrates that
may live 5–10 years and need to reproduce within these
time limits. By restoring natural flood frequency, the
loss of resting stages during dry periods is predicted to
balance egg production and hatching during floods,
resulting in timely booms of micro-invertebrates that
underpin native fish and waterbird recruitment after
floods.
Acknowledgements
We thank the landholders who generously gave their
time to this project and provided field accommodation.
We thank the State Wetland Action Group and the
Lower Murray Darling Catchment Management
Board for funding, the New South Wales National
Parks and Wildlife Service for logistical support, Gina
Dimcev for laboratory assistance and Ben Wolfenden
for contributions to figures. Three anonymous referees
provided useful comments on our manuscript. K. Jenkins
was supported by an ARC Linkage fellowship while
writing this paper.
Fig. 7. Conceptual model of ecological mechanisms by which
the restoration of flooding regime could achieve the target to
preserve micro-invertebrate community resilience by protecting
the egg bank.
831
Arid-zone river
restoration
© 2007 The Authors.
Journal compilation
© 2007 British
Ecological Society,
Journal of Applied
Ecology, 44,
823–832
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Received 9 May 2006; final copy received 11 January 2007
Editor: Paul Giller
Supplementary material
The following supplementary material is available for
this article.
Fig. S1. The Murray-Darling Basin (inset within
Australia), Darling River, Talyawalka Creek and lakes
on Teryaweynya Creek.
Table S1. Statistical Design for Analysis of Variance.
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... However, lake hydroperiods still need to be long enough and frequent enough for desiccation-resistant life stages to be produced so that propagule stocks are maintained (Strachan et al., 2015;Waterkeyn et al., 2008). Longer dry periods may increase vulnerability to local extinction through reduced viability of propagule banks in sediments (Eskinazi-Sant'Anna & Pace, 2018;Jenkins & Boulton, 2007). Shorter hydroperiods may leave insufficient time for invertebrates to reach dispersal life stages or may cause hatching or metamorphosis at inopportune times (Hairston & Kearns, 2002;Strachan et al., 2016a). ...
... Although remarkably flexible, the desiccation survival mechanisms used by aquatic invertebrates in seasonal lakes in southwestern Australia would not perform well with either very short or no hydroperiod (Strachan et al., 2014(Strachan et al., , 2016a(Strachan et al., , 2016b. One mechanism that many species rely on to survive the absence of surface water, desiccation-resistant eggs, is highly effective for surviving dry periods of <5-10 years but shows marked decline over longer dry periods in field studies (Eskinazi-Sant'Anna & Pace, 2018;Jenkins & Boulton, 2007). Consequently, it appears conditions across this region are exceeding the capacity of many species to adapt, leading to the observed large decline in γ diversity and increased likelihood of widespread extirpation (and potentially extinction). ...
Article
Many regions across the globe are shifting to more arid climates. For shallow lakes, decreasing rainfall volume and timing, changing regional wind patterns and increased evaporation rates alter water regimes so that dry periods occur more frequently and for longer. Drier conditions may affect fauna directly and indirectly through altered physicochemical conditions in lakes. Although many studies have predicted negative effects of such changes on aquatic biodiversity, empirical studies demonstrating these effects are rare. Global warming has caused severe climatic drying in southwestern Australia since the 1970s, so we aimed to determine whether lakes in this region showed impacts on lake hydroperiod, water quality, and α, β and γ diversity of lake invertebrates from 1998‐2011. Seventeen lakes across a range of salinities were sampled biennially in spring in the Wheatbelt and Great Southern regions of Western Australia. Multivariate analyses were used to identify changes in α, β and γ diversity and examine patterns in physicochemical data. Salinity and average rainfall partially explained patterns in invertebrate richness and assemblage composition. Climatic drying was associated with significant declines in lake depth, increased frequency of dry periods, and reduced α and γ diversity (γ declined from ~300 to ~100 taxa from 1998‐2011 in the 17 wetlands). In contrast, β diversity remained consistently high, because each lake retained a distinct fauna. Mean α diversity per‐lake declined both in lakes that dried and lakes that did not dry out, but lakes which retained a greater proportion of their maximum depth retained more α diversity. Accumulated losses in α diversity caused the decline in γ diversity likely through shrinking habitat area, fewer stepping‐stones for dispersal and loss of specific habitat types. Biodiversity loss is thus likely from lakes in drying regions globally. Management actions will need to sustain water depth in lakes to prevent biodiversity loss.
... For example, it has been demonstrated that sediments that have been flooded within the past 1-7 years tend to yield more abundant and diverse microcrustacean assemblages than sediments that have not been flooded for a decade or more (Boulton & Lloyd, 1992;Jenkins & Boulton, 2007;Nielsen et al., 2013). Such patterns probably arise as a result of both viability declines over time and actual loss of eggs through deflation by wind during dry phases (Cáceres & Soluk, 2002). ...
... These findings contrast with several other studies in Australia and elsewhere that have found higher abundances and richness in floodplain soils that are flooded more frequently (Boulton & Lloyd, 1992;Jenkins & Boulton, 2007;Nielsen et al., 2013;Paidere, 2009). In these studies, it was argued that the higher abundances and richness of hatched microcrustacean assemblages were a result of decreasing egg viability and resilience over time. ...
Article
• Several studies of temporary floodplain wetlands suggest that flood history is important to microcrustacean egg bank composition and hatching responses. However, these studies have largely focussed on contrasts among less frequently flooded areas (areas flooded every year to areas flooded once every 10–20 years) and less is known about variation at the more frequently flooded end of the gradient (from multiple floods per year to once every 2 years). Similarly, the effects of flood duration on egg banks have not been examined in detail. Thus, this study examines spatial variation in microcrustacean hatching at higher flood frequencies and in relation to inundation duration. • Surface sediment samples were collected from dry anabranches of the Macintyre River floodplain in Australia during February 2018, with a range of flood frequency from approximately four times per year to one in 2 years. Anabranches were selected randomly from predefined flood frequency classes and clustered into three different flood history groups based on flood history variables. Soil samples were collected from deep and shallow locations within anabranches, with depth assumed to be a proxy for the duration of inundation. Sediment samples were inundated in mesocosms and hatched microcrustaceans sampled over 6 weeks. • Microcrustacean abundance and assemblage composition varied by sites, relative depth, and duration of inundation. There was no variation by flood history groups. Highest numbers hatched from the deeper areas of anabranches, which is assumed to reflect differences in the egg banks of deep and shallow areas due to the longer duration of inundation in deeper areas. Duration also influenced hatching response from the egg bank, with more microcrustaceans hatching per unit time in the first 2 and final 2 weeks of the 6-week trial than the middle 2 weeks. Species richness also varied by relative depth and duration of inundation with more taxa hatching from the deeper areas of anabranches. • The study highlights the critical influence of flood duration on hatching patterns of microcrustaceans from inundated sediments. Therefore, changes to flood duration have the potential to influence microcrustacean assemblages and thus further changes to trophic interactions in temporary floodplain wetlands.
... For example, the granular formulation of Diazinon was cancelled after it became clear that birds were ingesting the granules when foraging for food and grit (U.S. EPA, 2004a, b). Jenkins and Boulton (2007) identified that the length of time a stream is desiccated was the predominant factor influencing invertebrate mortality in floodplain lakes in Australia. This finding was then used to recommend water allocations to support ecological functions. ...
Chapter
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Causal thinking is an everyday activity. We all are confronted with questions of causation, whether to figure out why the car is making a funny noise or why a toddler is running a fever. Our fascination with investigating causes is reflected in the enduring popularity of detective stories and in the frequency of investigative reports in the news. Because causal inference is commonplace, a book on ecological causal assessment may seem unnecessary. However, causes are not always easy to determine. Ecosystems are complex; the factors we can influence interact with natural factors, random processes, and initial conditions to produce the effects that are observed. Taking corrective action to remedy an environmental problem before knowing its cause could target the wrong thing, depleting scarce resources and missing an opportunity to improve environmental quality. Formal processes for causal assessment, as described in this book, are particularly helpful when the situation is complex or contentious. A wellarticulated process guides the analysis of available data and optimizes further collection efforts. A transparent process helps others replicate results and is more likely to convince skeptics that the true cause has been identified. A consistent process helps meet legal and regulatory standards for reasonableness and ensures that scientific information contributes to these decisions. Perhaps most importantly, formal methods help to eliminate biases that arise because of the all-too-human tendency to make and defend causal judgments too readily. As aptly articulated by the physicist Richard Feynman, “The first rule of science is not to fool yourself—and you are the easiest person to fool.” We began this project with a practical purpose—to share useful methods and strategies for identifying causes of undesirable biological effects in specific places. Causal assessment is a challenging, often humbling, but endlessly fascinating endeavor. It begins with the intrigue of a good mystery— why did this effect happen? Success requires the persistence to figure things out and solid strategies for using the information that you have and getting more of the right kind of information that you need. We feel fortunate to have been involved with adapting existing methods and testing new approaches. It has led us to renewed study of our intellectual heritage of science and philosophy, the strengths and foibles of human cognition, and the underlying assumptions of different sampling designs and analytical methods. It has also allowed us to provide scientific assessments and advice on some of the more complex ecological problems of our times. We have drawn on our personal experiences and those of our colleagues to provide examples and to describe approaches for assessing causes of undesirable biological effects in ecological systems. Some of these effects have captured the public’s attention and concern: collapsing fisheries and bee colonies; bleaching coral reefs; endangered species; dwindling stream life; and kills of fish, birds, and bats. Behind these reports are scientists who monitor our ecological systems and carefully document when something is amiss. In the past 20 years, biological monitoring has become an essential part of the environmental management tool kit. Causal assessment is the next essential tool. When we wonder why a condition has worsened, causal assessment finds the explanation. We believe that this book provides sound advice for the near term. We hope that it will lead the way to future improvements in methods and applicable scientific knowledge. We also hope that our study of causal assessment in the context of environmental management advances the larger field of causal assessment and provides insights into how we all can improve our causal reasoning.
... For example, the granular formulation of Diazinon was cancelled after it became clear that birds were ingesting the granules when foraging for food and grit (U.S. EPA, 2004a, b). Jenkins and Boulton (2007) identified that the length of time a stream is desiccated was the predominant factor influencing invertebrate mortality in floodplain lakes in Australia. This finding was then used to recommend water allocations to support ecological functions. ...
... For example, the granular formulation of Diazinon was cancelled after it became clear that birds were ingesting the granules when foraging for food and grit (U.S. EPA, 2004a, b). Jenkins and Boulton (2007) identified that the length of time a stream is desiccated was the predominant factor influencing invertebrate mortality in floodplain lakes in Australia. This finding was then used to recommend water allocations to support ecological functions. ...
... stoneflies: Bogan, 2017;fishflies: Cover et al., 2015;caddisflies: Salavert et al., 2008) or fish (African lungfish: Fishman et al., 1986) or protective pigment and cell structures in algal and bacterial biofilms (Colls et al., 2019;Gionchetta et al., 2019;Robson, 2000). For example, Jenkins and Boulton (2007) showed that microorganisms such as rotifers and cladoceran could be found in sediments rewetted after a 20-year dry phase, but cladoceran abundances decreased drastically between their 6-year and 20-year dry phase treatments. These strategies, conceptualized as temporal dispersal (Buoro & Carlson, 2014), allow organisms to persist locally and recolonize quickly at rewetting, but strongly depend on the duration of the dry period. ...
Article
Intermittent rivers and ephemeral streams (IRES), those watercourses that periodically cease to flow or dry, are the world’s most widespread type of river ecosystem. Our understanding of the natural hydrology and ecology of IRES has greatly improved, but their responses to extreme events such as drought remains a research frontier. In this review, we present the state of the art, knowledge gaps, and research directions on droughts in IRES from an ecohydrological perspective. We clarify the definition of droughts in IRES, giving recommendations to promote transferability in how ecohydrological studies characterize droughts in non-perennial stream networks. Based on a systematic search of the literature, we also identify common patterns and sources of variation in the ecological responses of IRES to droughts and provide a roadmap for further research to enable improved understanding and management of IRES during those extreme hydrological events. Confusion in the terminology and the lack of tools to assess the hydrological responses of IRES to drought may have hindered the development of drought research in IRES. We found that 44% of studies confused the term drought with seasonal drying and that those that measure droughts in a transferable way are a minority. Studies on ecological responses to drought in IRES networks are still rare and limited to a few climatic zones, organisms and mainly explored in perennial sections. Our review highlights the need for additional research on this topic to inform IRES management and conservation.
... These inter-basin transfers and dams have numerous deleterious effects on stream insects (reviews in Boulton and Brock, 1999;Allan, 2004) and are the inevitable by-product of seasonal and supra-seasonal droughts when humans seek a more reliable surface water supply. Multiple small storages on feeder streams further disrupt longitudinal connectivity and reduce total runoff, rendering rivers downstream more drought-prone than normal and leading to longer periods when floodplains remain dry, with negative impacts on the aquatic biota (review in Jenkins and Boulton, 2007). ...
Chapter
This book considers some of the potential influences on individuals and populations (e.g. environmental stresses, parasites, cannibalism, dispersal limitations), the 'cunning tricks' used by aquatic insects to overcome challenges (e.g. polarization vision, life-history strategies, osmoregulation, cold hardiness) and the consequences of those challenges at different levels of organization (e.g. distribution patterns, population structure, population genetics, evolution).
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The seasonal inundation of floodplains facilitates lateral connectivity allowing organisms to move into previously inaccessible habitats for feeding, foraging and reproduction. This serves to increase ecosystem productivity of floodplain and instream ecosystems that help maintain biodiversity and productive freshwater fisheries. Beyond freshwater habitats, the importance of flow and floodplain inundation to coastal ecosystems and marine fisheries is well documented. For example, freshwater flows to estuaries and coastal zones deliver nutrients and alter salinity regime, increasing densities of prey species as well as facilitating the migration of target species of fisheries from freshwater and floodplain systems into the marine environment. As such, conserving the ecological integrity of rivers and floodplain systems is crucial to maintaining these ecosystem services (Ndehedehe et al. (2021) Ecol Indic).
Article
Human intervention through damming, diversion and extraction of water resources has created regulated dryland river systems. As a result, connectivity between river channels and floodplain wetlands has diminished. Wetland function is fundamentally linked to water availability: flooding exchanges water, nutrients, sediments and biota with the floodplain. Water allocation for environmental flows may mitigate wetland degradation following river regulation by improving hydrological connectivity between rivers and floodplain wetlands. We report the results (2014–15 to 2018–19) of a vegetation monitoring program in the Macquarie Marshes in north western New South Wales. As part of the long‐term program, we monitored semi‐permanent wetland (Water Couch (Paspalum distichum) grassland or sedgeland dominated) and River Red Gum (Eucalyptus camaldulensis) forest/woodland communities along with environmental and water resource availability predictors. During the five‐year period, we found linear and nonlinear responses of functional group abundance and species richness to the water year and to time since last inundation. We also found differences in species assemblages in response to the flow and flooding regime, particularly water year and inundation duration. These results indicated that wetlands continued to express dry and wet phase responses. We also observed a depressed response to the large 2016–17 flood event by a subset of semi‐permanent wetland sites that had not been inundated in 3 years, compared with sites that were more recently inundated. This result indicated that environmental water management, along with protection of natural inundation events, may improve the resilience of floodplain wetlands: increased hydrological connectivity may promote a stronger wetland response when floods occur. Our results indicate that inundation, in part comprised of managed environmental flows, is a primary driver of species assemblage and functional group representation in semi‐arid floodplain wetlands.
Article
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Ponds rehabilitation projects for the purpose of eco - rehabilitation following significant anthropogenic impacts or degradation are becoming more frequent but not always successful. Therefore, the experience of the restoration of the Lebyazhye system lakes in Kazan city (Russia) is interesting. Previously, the lake system used to consist of four ponds, but due to water catchment area reduction, the area of the lake system also decreased, and only one lake remained. The restoration of the Lebyazhye system lakes was carried out in 2017 and included the deepening of the basin of the Bolshoe and Svetloe Lebyazhye lakes to 4 m, the sealing of the bed of future ponds with bentonite mats, supplying water from Izumrudnoye lake through a pressure water conduit and filling the basin of the lakes with water. The research is devoted to the study of the restoration of zooplankton communities in the Lebyazhye system lakes. For this purpose, the indicators of zooplankton communities before and after eco-rehabilitation measures were compared. After the implementation of eco-rehabilitation measures, significant changes in environmental parameters were observed: the salinity of water decreased, the oxygen content in the water, pH increased. In zooplankton communities, the species richness and diversity increased, new species appeared, as well as those that lived in the lake system earlier before eco-rehabilitation measures were taken.
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Renewable fresh water comprises a tiny fraction of the global water pool but is the foundation for life in terrestrial and freshwater ecosystems. The benefits to humans of renewable fresh water include water for drinking, irrigation, and industrial uses, for production of fish and waterfowl, and for such instream uses as recreation, transportation, and waste disposal. In the coming century, climate change and a growing imbalance among freshwater supply, consumption, and population will alter the water cycle dramatically. Many regions of the world are already limited by the amount and quality of available water. In the next 30 yr alone, accessible runoff is unlikely to increase more than 10%, but the earth's population is projected to rise by approximately one-third. Unless the efficiency of water use rises, this imbalance will reduce freshwater ecosystem services, increase the number of aquatic species facing extinction, and further fragment wetlands, rivers, deltas, and estuaries. Based on the scientific evidence currently available, we conclude that: (1) over half of accessible freshwater runoff globally is already appropriated for human use; (2) more than 1 x 10(9) people currently lack access to clean drinking water and almost 3 x 10(9) people lack basic sanitation services; (3) because the human population will grow faster than increases in the amount of accessible fresh water, per capita availability of fresh water will decrease in the coming century; (4) climate change will cause a general intensification of the earth's hydrological cycle in the next 100 yr, with generally increased precipitation, evapotranspiration, and occurrence of storms, and significant changes in biogeochemical processes influencing water quality; (5) at least 90% of total water discharge from U.S. rivers is strongly affected by channel fragmentation from dams, reservoirs, interbasin diversions, and irrigation; and (6) globally, 20% of freshwater fish species are threatened or extinct, and freshwater species make up 47% of all animals federally endangered in the United States. The growing demands on freshwater resources create an urgent need to link research with improved water management. Better monitoring, assessment, and forecasting of water resources will help to allocate water more efficiently among competing needs, Currently in the United States, at least six federal departments and 20 agencies share responsibilities for various aspects of the hydrologic cycle. Coordination by a single panel with members drawn from each department, or by a central agency, would acknowledge the diverse pressures on freshwater systems and could lead to the development of a well-coordinated national plan.
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The spatial and temporal aspects of dormancy in a freshwater copepod, Diaptomus sanguineus, were investigated during three consecutive years in Bullhead Pond, Rhode Island. Patterns of diapausing egg production and deposition were monitored with plankton sampling and settling traps. Vertical and horizontal distributions of diapausing eggs in sediments were investigated by taking core samples. Diapausing eggs removed from sediments were tested in the laboratory for hatching ability. The long-term spatial and temporal patterns of emergence from the diapausing egg stage were documented in the field using inverted plastic funnel traps sampled weekly. The field data along with an estimated annual budget for diapausing eggs in the pond suggest that D. sanguineus has an egg bank, analogous to the seed banks of plants, that allows it to survive through harsh environmental periods.
Article
Aquatic ecosystems in dry areas are important elements of the planetary hydrological environment. Greater knowledge of them would undoubtedly expedite not only their better local management, both as a resource and a hazard, but also be of wider use in the future, given likely global climatic changes, recent expansion of "desertified' areas, and the accelerating use (and therefore potential depletion) of surface waters in areas where water has not yet limited human population growth and activity.. The definitive account of the limnology of dry areas has yet to be written. This chapter serves as a useful introduction to it! -from Authors
Article
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.
Book
1. Introduction 2. Estimation 3. Hypothesis testing 4. Graphical exploration of data 5. Correlation and regression 6. Multiple regression and correlation 7. Design and power analysis 8. Comparing groups or treatments - analysis of variance 9. Multifactor analysis of variance 10. Randomized blocks and simple repeated measures: unreplicated two-factor designs 11. Split plot and repeated measures designs: partly nested anovas 12. Analysis of covariance 13. Generalized linear models and logistic regression 14. Analyzing frequencies 15. Introduction to multivariate analyses 16. Multivariate analysis of variance and discriminant analysis 17. Principal components and correspondence analysis 18. Multidimensional scaling and cluster analysis 19. Presentation of results.
Article
Observations on populations of Branchinecta mackini in temporary ponds, which last for as little as 3 days to as long as 4 months, on a desert playa showed that hatching of dehydrated cysts (eggs) follows initial entry of water into the basin if salinity remains low. Salinity ranges from an initial 0.5% to as much as 34% as the pond evaporates. Hatching is continuous at constant low salinity, but since salinity general increases rapidly, initial hatch is usually of short duration. Additional periods of hatching follow further inflows of water or after meeting of ice, that is, after reductions in salinity. The duration of hatching is inversely proportional to rate on increase in salinity. When salinity of small-volume summer ponds increases at rates above 500 ppm (1,000 (mu)mhos) per day, three in virtual inhibition of hatching. Laboratory studies showed that egg hatching was controlled by both salinity and oxygen operating in various combinations to inhibit or stimulate hatch. The hatching characteristics obtained from laboratory cultures after ejection from ovisacs of living females. The finding that a salinity-oxygen complex regulates hatching in a desert pond permits tentative explanation of a difference between branchiopods of humid and arid regions. In both cases the branchiopods are characteristic of astatic waters, and stimulation of the egg to hatch must be by some factor that changes at the time or origin of the temporary pond. In humid regions the factors of concern are temperature and oxygen. If the water undergoes significant changes in salinity, as it does in arid regions, control of egg hatch may be by both salinity and oxygen, with temperature limited to control of rate of development.