A Natural History of Millbrook Marsh,
A Wetland In An Urbanizing Setting

Discussion

Basically, the morphology of Millbrook Marsh streams, with the exception of the two branches of Bathgate Spring Run, has been and is still being negatively affected by stormwater input. High velocity, excessive amounts and erratic input of stormwater have caused streambank erosion and high sedimentation rates on the stream bottoms. The results of the excessive stormwater input are wide reaching. High siltation causes habitat degradation for benthic macroinvertebrates, resulting in lowered species diversity and species richness (Chapter 6). Benthic macroinvertebrates are part of the food supply for fish, amphibians, reptiles, some birds and mammals, so the stormwater input indirectly affects the populations of these species as well. In addition, herbaceous riparian vegetation has decreased or been eradicated, as seen in some reaches of Slab Cabin Run and Thompson Run. Another possible effect is the lowering of the water table, which affects vegetation types in the marsh as a whole. Essentially, the stormwater entering Millbrook Marsh has most likely been the initial cause of many of the changes within the system.

The parameters of water quality that are generally affected by sewage treatment plant (STP) effluent have improved since 1983. The sporadic fish kills that occurred before 1983 were due to either STP effluent or stormwater. Fish kills have occurred after 1983 due to stormwater alone. The stormwater input is still affecting water quality. Water quality testing must be done during and after storm events to gather enough data for comparison to historical data, and to determine whether levels of contaminants are below the acceptable limits for the protection of aquatic life. Historically, dissolved oxygen levels have varied. Only in June 1962 was the level below the minimum 5.0 mg/l in Slab Cabin Run, but Thompson Run was close to that minimum in October and November 1960. There is no data available for Thompson Run or Lower Slab Cabin Run after the STP effluent ceased in Thompson Run. Water samples that include stormwater from Thompson Run should be tested for dissolved oxygen levels to enable comparison. Turbidity data is sparse, but the high level of turbidity in 1980 in Upper Slab Cabin Run reflects stormwater input. Another point is that JCU’s are inaccurate under a turbidity level of 25 though the 1978 report shows 5 JCU and 6 JCU. It was not above the acceptable limits for CWF aquatic life. There is not enough Kjeldahl nitrogen data for comparison. The ammonia nitrogen data is sparse, but levels seem to have decreased from 1959 to 1989 in both Thompson and Slab Cabin Runs. Nitrate levels, on the other hand, have increased in Thompson Run from 1960 to 1989. The lower pH levels in Millbrook Marsh streams could be reflective of rain before the water sample was taken, but this is not indicated except in the case of the 1980 PennDOT data. The levels of pH were very low, due to the high amount of rainwater in Slab Cabin Run. The pH at that time was more acidic than allowed for a CWF stream with the designated use of protection of aquatic life. The level of phosphorus was much lower in 1989 than in 1960, and the levels of phosphate and orthophosphorus were very high in the 1960’s as well. Phosphorous levels were most likely particularly high at that time because of much wider use then than now. The high phosphorus levels in Thompson Run and Lower Slab Cabin Run were probably due mainly to the STP effluent input. The only phosphorus data available for Thompson or Lower Slab Cabin Run is from July 1989, and reflects a significantly lower total phosphorus level. Chloride levels were not exceeded for water bodies designated for recreational use or use as a water supply. More testing should result in a better data set for comparisons of STP effluent influence and stormwater influence on water quality in Millbrook streams, though it is evident in the water quality data gathered after 1983 that the streams have improved since the cessation of treated sewage effluent input. Continued and increasing stormwater input is also very clearly affecting the water quality and stream conditions at Millbrook, and therefore, affecting the flora and fauna of the marsh. This is apparent when looking at the 1980 PennDOT report, since the sampling stations were on Slab Cabin Run above the confluence with Thompson Run, and so did not include sewage effluent. The data was gathered after 2 days of rain in State College. The stormwater input had significant impact upon the results. The high turbidity levels were due to being sampled immediately after the rain, before the stream had time to recover from the sediment load from runoff. Chloride levels were probably influenced by proximity to State College. Sodium levels were affected by the use of road salts in winter, transported into Slab Cabin Run with stormwater runoff. The very high fecal coliform counts, substantially higher than the state and Federal standards for bathing water at 200 cts/100ml, were attributed to runoff from parts of State College, Dalevue and Lemont neighborhoods, septic tank leachates, and stormwater runoff from the nearby streets and pastures during the previous rain. The stormwater runoff also carried petroleum products from the roads and caused the very high levels of oil and grease in the stream. The unusually low pH of the streams, 5.8 and 6.0 instead of 7.6 to 8.7 in Slab Cabin Run, was most likely caused by large amounts of acid rainwater added to the streams. Pennsylvania receives the largest amount of acidic precipitation in the United States, with an average pH of almost 4 (Thorne et al. 1995). In 1980, acid rain in State College was usually between 3.5 and 5.0 (PennDOT 1981). Ten years ago, the pH of State College area rain was usually about 4.5. This has declined to a pH that is commonly now about 3.5 (S. McGonigal, pers. comm.).

Phosphorus is contributed not only by the sewage effluent, but also by the stormwater from agricultural and residential lands and the use of fertilizers and other chemicals, animal wastes, litter, and decaying vegetation. The data from 1980 included only stations located on Slab Cabin Run above its confluence with Thompson Run, and therefore, the high levels of contaminants resulted from field and street runoff from Dalevue, Lemont, parts of State College, and the associated on-lot sewage facilities (septic systems) there. Consequently, the levels in the 1980 data are representative of stormwater runoff, rather than the sewage treatment plant effluent.

Levels of contaminants in Thompson Run and Slab Cabin Run below the confluence were not tested after a period of rain, but it would be reasonable to believe that levels would be higher than those of Slab Cabin Run above the confluence due to the greater amount of urban drainage area stormwater coming from State College borough and the Penn State campus. Discontinuation of sewage effluent input lowered the phosphorus levels of Thompson Run and downstream waters, but some phosphorus loading is most likely occurring from the stormwater input, as seen in the 1980 phosphorus data for Slab Cabin Run from the PennDOT study.

. The number of stormwater inputs has increased since 1980, as has the amount of developed land, roads, other impervious surfaces, and hence, the total stormwater amount has increased as well. Levels of turbidity, total suspended and dissolved solids, fecal coliform bacteria, contaminants associated with fertilizers and pesticides, oil and grease and other road surface materials and low pH will continue to increase with increases in stormwater input, and possibly resulting periodic fish kills and water quality impairment from accidental spills or other sporadic contamination from stormwater, as has happened in the past.

  On to Chapter 4