Ten Towns Committee
Macroinvertebrate Sampling - 2002
 
The Macroinvertebrate Communities of
the Great Swamp Watershed:
June, 2002: Results

A Report to the
Ten Towns Great Swamp Management Committee

Leland W. Pollock, Ph.D.
Department of Biology
Drew University

October, 2002

Executive Summary
The impact of upstream impoundments on macroinvertebrate communities continues to be variable and frequently detrimental..  This year, environmental conditions and the community quality at GB5 (below Foote's Pond) improved, PR1 (below Osbourn Pond) remained unchanged but "poor", while LB2 (below Loantaka Pond) declined alarmingly.  Elevated temperatures, reduced oxygen, and spill-over nutrients/productivity from ponds appear to be the likely source of these changes.  In addition, impoundment-related sedimentation events in the past have made major impacts on GB3 (below Silver Lake) and PB3 (below a small pond) and appear now to still influence the recovery of community quality at downstream sites, GB2 and PB2.  Understanding and controlling nutrient driven productivity in these impoundments and avoiding sedimentation events could lead to improvements in stressed downstream localities.  Otherwise, upstream sites in the watershed's western streams, Primrose Brook and the Passaic River, continue to do well.

Black Brook localities represent special but different cases, neither are likely to improve substantially.  Loantaka and Great Brooks remain sources of concern.  Low gradient, sluggish water flow, heavy sedimentation, and lack of suitable macroinvertebrate habitat appear to account for most of the poor macroinvertebrate indicators in both the Loantaka and Great Brooks.  Very high TDS readings continue to characterize all sites along Loantaka Brook in a high-lower gradient from farthest upstream to downstream locations.

The June 2002 Great Swamp Watershed Study: Results
An general introduction and descriptions of methods used in this survey are available elsewhere at this site.
Habitats & Environmental Monitoring
On June 11, 2002, we monitored environmental conditions at all 17 sites between 9 am and 3:30pm.  Refer to Table 02-1 for site-specific values for these variables.  Figure 02-1A & 02-1B offer mean values and ranges represented by the 17 sites in this Great Swamp Watershed survey (note that temperatures shown must be doubled, TDS readings multiplied by 50, and Habitat Values must be multiplied by 5 to yield their true values).  The spread in total dissolved substances (TDS), temperature, and Habitat Values is especially noteworthy because these factors are presumably subject to human influence, through added chemicals, interruption of the overlying tree canopy (via impoundments or riparian alteration), and habitat limitations primarily through the introduction of sediments/silt respectively.  Results shown in Figure 02-1A & B are similar to those reported in the 2001 survey, although the high turbidity readings seen in 2001 were absent in drought-prone 2002.  These observations underscore the continuing cause for concern regarding the impact of human disturbance within the Great Swamp watershed.  Patterns can be seen by reviewing key variables individually during this 2002 survey (in Table 02-1) and in comparison to observations from the previous two years (in Table 02-2).  Predictably, sites displaying highest temperatures - > 24 C in 2002 - (i.e., BB1, LB2, GB3, GB5, PR1) are all immediately downstream from dammed impoundments.  The pattern noted in 2001 of strikingly high values for total dissolved substances (TDS > 500 ppm) at all the Loantaka Brook sites continues in 2002.  It is important to note that values increase upstream, a trend that a preliminary investigation shows continues even above LB4, the most upstream site in this survey.  Highest TDS values occur upstream from Loantaka Pond, the Morris Township sewage treatment plant, the Seton Hackney riding stables, and the community swimming pool at Fanok Road, suggesting that although any or all of these may contribute to stream conditions, none are the primary source of high TDS observed in recent years.  The actual upstream source and the identity of these high levels of TDS is unknown.  This year, the Great Brook sites showed a similar trend of increasing TDS upstream, although values were only half those found in Loantaka Brook.  Less disturbed sites throughout the watershed had TDS values less than 200 ppm.  These patterns precisely match those from previous summers. 

Compared to generally high values in June, 2001, dissolved oxygen values were more modest this summer.  Ambient temperatures (somewhat warmer this year) and several variables related to plant productivity shape overall dissolved oxygen values, making patterns within the streams more informative than are absolute levels.  All sites with lowest DO levels were found in more heavily stressed, slower moving, eastern watershed streams while higher values were typical of western watershed streams.  DO tends to decrease from headwaters downstream.  Low DO exceptions to this occur in particularly sluggish flow (e.g., GB4, often at LB4), while higher exceptions can occur downstream from productive impoundments (e.g., LB2, GB3).  As in the past, no discernable pattern was observed in the stream site distribution of pH or turbidity, except that turdibity was very low in June 2002 during this low rainfall year. 

Most habitat assessment scores match expected trends of increasing quality along an east to west gradient across the watershed.  While variability might be expected in this cumulative, subjective evaluation of habitat conditions, it is interesting to note that lower quality (i.e., eastern) sites have shown greater variability over the years (see Table 02-2) than have higher quality (i.e., western) sites.  It makes sense that these measures, emphasizing erosion and sedimentation, vary more in the impacted streams.

Macroinvertebrate Survey
B-IBI and Beck Index scores for macroinvertebrate communities are shown in Fig. 02-2.  As usual, they match fairly well.  Compared to locally generated B-IBI values, the organic pollution based Beck Index consistently offers a more optimistic view of Great Brook sites and a poorer view of the generally higher quality upstream-most sites.

A comparison between B-IBI values for 2002 and 2001 is given in Figure 02-3.  In an attempt to differentiate noteworthy changes in conditions at particular sites from the "normal" range of variation, I have plotted lines representing one standard deviation above and below the mean values of each site in Figure 02-4.  Data points lying beyond these lines should attract attention, as should scores changing by four or more B-IBI points.  Reasons for these changes can be identified from among the eight components used to calculate the B-IBI value in Table 02-3.  It may be easier to visualize these specific differences by referring to summary Table 02-4.  Note that in nearly all cases, declines still fell within the - 1 Standard Deviation limits shown in Fig. 02-4.

Loantaka Brook sites LB1 and LB3 are among those showing greatest decline.  In both cases, scores have been limited to a fairly narrow range of values, with changes based on the presence or absence of certain key species.  Shifts noted here reflect declines in total taxa present along with an increase in the number of stress-tolerant species.  In neither case is the change especially alarming. 

The community at PB2 dropped by four points from composition changes that included a decline in caddisfly (Trichoptera) species and a drop in the proportion of the community represented by predators.  The change was due to a decline in caddisfly (Trichoptera) species, in the proportion of the community represented by predators, an increase in the number of pollution-tolerant species and in community dominance by the two most abundant species.  In fact, the June, 2002 rating is close to matching that of June, 2000, suggesting that perhaps June, 2001 was an unusually good year for the macroinvertebrate community there. 

Meanwhile, GB5, PR2 and PR3 all increased significantly in community quality.  Increased species present, especially among caddisflies improved the dominance structure at GB5.  This year the abundant green algal growth, visible in the past at this location just below sluggish, productive Foote's Pond, was much less dense.  The condition of Foote's Pond appears to directly influence the GB5 community.  Dominance declined strikingly as the community was no longer comprised primarily of the caddisfly larva, Cheumatopsyche and blackfly larvae as was the case in June, 2001.  More species were found this year (i.e., 21 vs. 16 species), including more that were intolerant of pollution and fewer of which were tolerant.  This site may continue to show variability however because of its proximity and dependence on fluctuating productivity in the impoundment just above it.  Increases in the number of caddisflies and stoneflies helped the Passaic River sites to improve in score this year.

Although neither of the following showed a large enough change in B-IBI score to be included in the analysis above, two other sites are important to highlight.  LB2 and GB4 saw 50% decline in species present between June, 2001 and June, 2002.  GB4 suffers from very poor habitat conditions at best little water flow, sparse hard substrate to attach to, etc.  This poor rainfall year undoubtedly contributed to sluggish water flow, higher temperatures, and thus lower dissolved oxygen levels.  As a result, this decline, effectively making a poor site worse, should not be surprising. 

The LB2 site is situated 100 yds downstream from Kitchell Pond and shows a greater range of variation in B-IBI scores than any other site in the study.  Most disturbing is the steady and significant decline in scores over the past three years, a circumstance matched by the observed progressive buildup of excessive algal growth at LB2.  Although nutrient data have not been gathered in this survey, increasing algal growth, such as that seen at LB2, is usually associated with nutrient increase.  Higher DO and pH values in the past two years (see Table 4) are consistent with increased productivity at or above this site.  The highly productive Loantaka Pond immediately upstream may have served as something of a nutrient sink in the past.  Precise factors responsible for possible changes in nutrients at LB2 remain unknown.  Although it's B-IBI value did not exceed one standard deviation, another noteworthy change in June, 2002 was PB 2 which fell considerably from its high rating in June, 2001.

For comparison to earlier studies of macroinvertebrate communities at these sites, adjusted Beck scores for 2002 have been added to Table 02-5.  Changes in evaluative techniques between the initial 1992-1999 surveys and the 2000-2002 surveys are at least partly compensated for by adjusting scores as describe in the table.

Combining Habitat Assessment and Biotic Metrics
To gain a broader perspective on the ecology of Great Swamp Watershed streams, it is useful to view the distributions of environmental variables and of biological communities together.  (A brief discussion of the relationship between the recent Great Swamp Water Quality Report (Leib and Browne, 2002) and results of these macroinvertebrate surveys can be found in Appendix 02-2).  While it is difficult to determine precise cause and effect relationships between specific conditions present and the collection of organisms they support, there are a couple of ways to at least view the correlations that exist between these two entities.
Correlation Analysis
The results of correlation analysis between biotic metrics and stream site conditions are found in Table 02-6.  Correlation coefficients (r) display the degree to which changes in the measured level of each habitat variable at the 17 sites study matches the distribution of biotic metric value calculated on the basis of the macroinvertebrate community found at these locations.  Comparing habitat and metrics for 17 sites, and selecting the standard 95% certainty level to determine significance, correlation coefficients > + 0.482 (df = 15; p <0.05) show significant correlation.  It is important to stress that correlation shows only that the two entities being compared co-vary.  It does not necessarily demonstrate a causal relationship.

In Table 02-6, I have used a box and bold type to highlight statistically significant correlations between the two biotic indexes calculated here, Beck and B-IBI, and environmental variables monitored on June 11, 2002.  First, it is reassuring that the metrics are highly correlated with one another ( r = 0.934).  But they also both show matching correlations with most other variables.  B-IBI values show significant negative correlation with temperature and total dissolved substances (TDS), i.e., as temperature or TDS increases, the corresponding values for the metrics decrease.  High positive correlations are found with riparian vegetational cover (veget), the frequency of riffles (riffl), the degree of freedom from sedimentation (sedim), and the degree to which stones escape becoming embedded in sediments (embed).  As these important habitat features improve, so does the community index.

It is particularly interesting to note that the highest correlations are between B-IBI values and stream gradient and habitat value.  As shown in Table 02-6, both these variables are strongly correlated with almost all other variables.  Gradient, shown to be strongly correlated with B-IBI values in Figure 02-5, influences stream flow which in turn influences erosion (i.e., bank stability, cover, habitat regimes, vegetational cover), sedimentation (i.e., embeddedness, sediments, riffle frequency), and other critical conditions (e.g., temperature, TDS, DO).  It is probable that limitations on gradient set by the natural "lay of the landscape" may place environmental limitations on many other variables and thereby cap the maximal macroinvertebrate community quality that one can expect at a given site.

Habitat Values are compared to B-IBI values in Figure 02-6 for June, 2002.  By regarding positions of various sites relative to the least-squares, best-fit regression line (and +/- one standard error of the mean estimate) added to the figure, we can identify some sites as having higher habitat scores than is reflected by the biotic community present (i.e., points well below the regression line) while others have surprisingly high community quality given their Habitat Value (e.g., points well above the line).  This may prove to be a valuable tool for identifying sites of particular concern.  If a site consistently falls well below the line, we might explore reasons for poor biological community development there.  For example, GB3 has fundamentally good habitat characteristics but is still recovering from a major perturbation from the dredging of Silver Lake, just upstream, in 1998-1999.  In 2002, LB2 had basic habitat characteristics theoretically capable of sustaining a biotic community at the B-IBI = 16 level as it did in 2001.  Conditions beyond those included in calculating its Habitat Value are presumed to be associated with its decline recently as has been discussed above.

Similarly, sites consistently above the line appear to be hosting a biotic community "beyond their means".  The danger in these settings could be that their communities may be at risk of falling to levels more commensurate with their habitat quality.  The question to ask at these sites is what conditions other than those contributing to the Habitat Value have encouraged their stronger than expected community development.  In similar vein, some sites, such as PR2 and LB3, persist in hosting a richer community than can be explained by their Habitat Value characters alone.

Significant correlations among the environmental variables themselves are also shown by boxes and bold type in Table 02-6.  One factor within these data stands out because its surprising lack of high correlations.  The extent of riparian cover correlates only with stream order.  In fact, this variable was only very weakly negatively associated with TDS and turbidity, although one might have expected that as the width of the riparian vegetational buffer increases, significantly less dissolved substances and sediments would appear in stream flow.  Riparian width also shows only weak positive relation to bank stability and stream bank vegetational cover.  There are at least two possible explanations for these rather unexpected results.  Sites within directionally flowing aquatic systems are likely to be more influenced by conditions upstream from them than by conditions immediately adjacent to them.  Also, the present of storm drains, frequent road crossings, and periodic breaches of riparian cover may undermine the positive influence of riparian cover elsewhere.

Stream Summaries
For the most part, macroinvertebrate communities reviewed during the 2002 sampling fell into patterns familiar from the previous seasons of study.  The range in environmental conditions and in macroinvertebrate communities is very wide in the Great Swamp watershed, underscoring the challenges before us in improving the stressed streams toward the east side and in preventing the deterioration of those more pristine sites to the west side of the watershed.
Indian Grave Brook (B-IBI rating was "good"):
This reference site remained in fine shape producing high B-IBI and Beck values. Environmental conditions here are close to ideal.
Passaic River (The PR1 sites rated "poor"; PR2 rated "fair"; PR3 rated "good"):
B-IBI values improved over last year at the upper two Passaic River sites.  PR1 remained low with environmental conditions reflecting the modifying influence of upstream Osbourn Pond (higher temperatures and TDS, lower dissolved oxygen).  Its gradient is particularly low as well.
Primrose Brook (PB1 was "fair"; PB2, PB3 were "good"):
PB1 and PB2 retreated somewhat from their record high B-IBI values last year.  PB3, on the other hand, improved.  Despite modest annual shifts up and down in B-IBI values, Primrose Brook remains overall the highest quality stream in the watershed from the macroinvertebrate standpoint.
Great Brook (GB3, GB5 earned a "poor" B-IBI rating; GB2, GB4 were "very poor"):
After a discouraging year for Great Brook in 2001, two sites, GB3 and GB5 showed marked improvement in 2002.  Both sites have varied considerably in the past and probably reflect changeable influence of impoundments just above them.  Warmer temperatures from stalled water mean lower dissolved oxygen.  Their biota may be modified by variable competition from overflow pond dwellers such as snails and amphipods.  GB4 may be hopelessly limited from substantial improvement by poor habitat constraints.  Unfortunately, no better habitat site has been located between GB5 and GB3.  GB2 may still be working through excessive sediment loading from the Silver Lake dredging project of 1998-1999.  The source of periodically elevated TDS levels at upper streams sites on Great Brook should be investigated.
Loantaka Brook (all sites earned "very poor" B-IBI ratings):
Upstream sites, LB3 and LB4, and LB1 all remained similar to their dismal B-IBI values from the recent past.  The steep decline in the macroinvertebrate community at LB2, below Loantaka Pond, was the greatest at any site in 2002.  This area has been showing a pattern of rising temperatures and TDS levels along with a visible increase in the abundance of algal growth.  Negative influence from the upstream Loantaka Pond is suspected in the decline of conditions at LB2.
Black Brook ("very poor" overall B-IBI rating):
Both Black Brook sites continued to fare poorly in 2002, but for different reasons.  BB1 has poor gradient and flow, low habitat value and dissolved oxygen levels, and high temperatures.  It is downstream and surrounded by a golf course.  BB2, just below the Chatham Township sewage treatment plant, has much better habitat, dissolved oxygen, and temperature characteristics, but slumped in B-IBI rating this year by being overrun by amphipod crustaceans (93% of the fauna).  Amphipods flourished this year both in the Great Swamp and Rockaway River watersheds.  These hardy animals may fare better in variable water conditions during this severe drought period.  The decline at BB2 may well be reversible with a return to more normal weather conditions. 
The June 2002 Great Swamp Watershed Study:  Recommendations
  1. This study marks the start of a second decade of macroinvertebrate community data from the streams of the Great Swamp watershed.  This valuable "history" of conditions within the water shed should be continued.
  2. Year to year variability in productivity and conditions of mid-stream impoundments appears to directly impact macroinvertebrate communities and thus, stream health downstream.  Understanding and controlling excessive nutrient driven productivity of these impoundments (especially at Kitchell Pond on Loantaka Brook, Foote's Pond on Great Brook, and Osborn Pond on the Passaic River would stabilize these stream sites.
  3. It seems apparent that stream bank erosion coupled with storm drain runoff lead to the sediment burial of desirable, coarser substrate habitat.  To echo suggestions made from various sources, and to quote my own comments from the 2000 survey, "it would have to help to provide adequate riparian buffers and to stabilize erodable banks along these streams as well as to devise ways to intercept and more gradually release storm water runoff to moderate their boom-or-bust flow regimes.  I realize that these are large scale solutions that, as usual, are much more easily said than done.  But without eventually dealing with these stream-wide, problem-defining causes, I am not sure how much improvement over current conditions we can expect to see at individual sites."
Literature Cited

Barbour, M.T., J.Gerritsen, B.D.Snyder, and J.B.Stribling.  1999.  Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, Second Edition.  (EPA 841-B-99-002).  U.S.  Environmental Protection Agency; Office of Water; Washington, D.C.

Karr, J.R.  and E.W.  Chu.  1999.  Restoring Life in Running Waters: Better Biological Monitoring.  Island Press, Washington, 206 pp.

Leib, A.S. and F.X. Browne.  2002.  Great Swamp Watershed Water Quality Monitoring Report.  F.X. Browne, Lansdale, Pennsylvania, 29 pp. + 5 appendices.

Pollock, L.W.  2001.  The Macroinvertebrate Communities of the Great Swamp Watershed, Summer, 2001.  A Report to the Ten Towns Great Swamp Management Committee.

SCS Water Quality Indicators Guide: Surface Waters.

Acknowledgments
I wish to express my appreciation for the Ten Towns Great Swamp Watershed Management Committee's understanding of the value of using macroinvertebrate communities to document water quality conditions throughout the watershed.  In particular, I am grateful for their funding of this study.  In addition I acknowledge the generous, in-kind support of my home institution, Drew University, and faculty colleagues who have provided encouragement as well as the equipment and facilities necessary to the project's completion.  And finally, I am especially indebted to Jeffrey Galvin, my Drew student assistant during this project, for providing such reliable field and laboratory help, and for sharing is fine collection of recorded music while on the road.
Figures
Figure 02-1A & 02-1B.  Mean and range values for various environmental factors observed on June 11, 2002 at the 17 sampling sites within the Great Swamp watershed.  Note: temperatures shown must be doubled, values for total dissolved substances (TDS) must be multiplied by 50, and Habitat Values must be multiplied by 5 to yield actual values.  Temperature in oC, total dissolved substances (TDS) in ppm, dissolved oxygen (DO) in mg/L, pH in units, and turbidity in FTU (Forel turbidity units).  See text for calculation of Habitat Values.

Figure 02-2.  Comparison of Beck Index and B-IBI values for 17 sampling sites within the Great Swamp watershed, June, 2002.  Descriptive terms and limits shown refer to Beck Index values.

Figure 02-3.  B-IBI values for 17 sampling sites within the Great Swamp watershed, June, 2002, June, 2001, and June, 2002. Lines represent +/- one standard deviation from the mean value at each site.

Figure 02-4.  B-IBI values for 17 sampling sites within the Great Swamp watershed, June, 2002, June, 2001, and June, 2002.  Lines represent +/- one standard deviation from the mean value at each site.

Figure 02-5  Stream gradient is plotted against B-IBI value for each of the 17 sampling sites based on the June, 2002 sampling.

Figure 02-6 The composite Habitat Value for each site is plotted against B-IBI values based on the June, 2002 sampling.  Lines represent mean values and +/- one standard error of the mean estimates.

All Figures.     All Tables.     Appendix.


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Macroinvertebrate Sampling Study - 2002