A Report to the
Ten Towns Great Swamp Management Committee

October, 2002

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.

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.

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.

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.

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."

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.

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.