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Dividing Creek (DC-01 and DC-02)

About the site:

There are two stations located in the study area on Dividing Creek. Sampled since 2010, DC-01 is located just upstream of the crossing under College Parkway while DC-02 is upstream on Anne Arundel Community College property. Implementation of a wetland seepage system in the upstream reach containing DC-02 occurred a few weeks before biological sampling took place in 2016, although the sampling reach containing DC-02 was not directly impacted by the restoration activities. Approximately 27% of each site's drainage area consists of impervious surfaces.



2018 Summary Report:

Site DC-01
Time FrameBIBI (Condition)FIBI (Condition)RBP (Condition)
2018 Results2.43 (Poor)2.67 (Poor)135 (Supporting)
Cumulative Average (2010-2018)2.29 (Poor)2.00 (Poor)139 (Supporting)
3-year Running Average2.33 (Poor)2.00 (Poor)137 (Supporting)
Site DC-02
Time FrameBIBI (Condition)FIBI (Condition)RBP (Condition)
2018 Results1.29 (Very Poor)2.00 (Poor)139 (Supporting)
Cumulative Average (2010-2018)2.37 (Poor)1.78 (Very Poor)114 (Partially Supporting)
3-year Running Average1.67 (Poor)1.67 (Very Poor)131 (Supporting)
1) No data for 2015.

Benthic IBI:

Site DC-01: Located downstream of the reach restored in 2016, DC-01 is upstream from College Parkway and has a decidedly wetland character, likely due to the backwater created by the road crossing.

The 2018 BIBI score at this site is in the Poor range, at 2.43. This score reflects the same results as the last BIBI collected at this location (2017). The sample was dominated by chironomids, which comprised approximately 40% of the insects found in 2018, but only about 15% of the sample in 2017. Oligochaetes changed from approximately 45% of all insects found in 2017 to about 22% in 2018.. Clams were the other common group in 2018, representing about 15% of insects found and half the amount observed in 2017.. Past samples were largely dominated by oligochaetes with lesser amounts of chironomids present. It is unclear why this shift in organisms occurred in 2018, but it might be related to the restoration work that occurred upstream at DC-02. This is discussed further in the next section (Site DC-02.).

DC-01 Sample of Insects Collected by Sample Year

CY01 Bugs
Click to enlarge

Site DC-02This site is located upstream of DC-01 and within the footprint of the restoration project completed in 2016. The sampling reach is located in a stretch of channel between two areas where the channel was reconfigured into a series of riprap steps and large pools typical for implementation of a wetland seepage system. The sampling reach itself was not purposely converted into a pool area, but channel water depth has increased and the velocity has slowed due to the impacts of the downstream pool area. At its upstream end, the sampling reach included a constructed stone weir (a dam that raises water level) that created the pool just upstream of the site, but did not include the pool itself.

This site produced a BIBI in 2018 of 1.29, or Very Poor. This represents a large decline since restoration and it is much lower than both the cumulative average (2.29, Poor) and the three-year running average (2.33, Poor). It should be noted that the restoration work concluded only weeks before the 2016 sample was collected. With the exception of the upstream riprap step, the sample reach itself was not included in the construction activities. However, the stream reaches draining to and from the sampling reach were completely changed.

The distribution of insects found in the 2018 sample seems to be synonymous with pre-restoration samples. All pre-restoration samples were dominated by chironomids, oligochaetes, and predacious diving beetles. The 2018 sample was very similar, but with much more damselflies, approximately 18% observed. Oligochaetes decreased to about 18% of invertebrates observed in 2018. The impact that a particular stream restoration project has on reaches downstream of the restoration is not well understood (Miller et al. 2010, McCabe and Gotelli 2000). However, it is possible that some aspect of the restoration work has had impacts on both sample reaches. It is also possible that there might be some unknown water quality impairment coming from upstream that caused this shift at one or both stations. The ultimate trajectory and persistence of any supposed change will require continued sampling at these locations.

DC-02 Sample of Insects Collected by Sample Year

CY01 Bugs
Click to enlarge

Fish IBI:

Site DC-01: The fish population appears to have improved, as a FIBI of 2.67 (Poor) was observed in 2018. This score represents an incline compared to the 2016 assessment, where this site scored a 1.33 (Very Poor) classification. Five species were observed in 2018: eastern mudminnow, golden shiner, eastern mosquitofish, American eel, and a goldfish , all of which are considered moderately tolerant of water quality impairments. The goldfish is a non-native species frequently found in Maryland streams. In 2016, the eastern mosquitofish was not found at this site, but the four other species found in 2018 were observed during the 2016 sampling.

Site DC-02: DC-02 also had an improvement in FIBI score in 2018 with a 2.00 (Poor) rating compared to a 1.33 (Very Poor) rating in 2016. Four species were observed at this location in 2018: eastern mudminnow, golden shiner, eastern mosquitofish, and goldfish. 

Physical Habitat:

Site DC-01: Habitat conditions have been consistent since monitoring began here in 2010. In 2018, a habitat score of 135 (Supporting) was calculated for this site, which is very consistent with the cumulative average (139, Supporting) and the 3-yr. running average (137, Supporting). High levels of bank stability and vegetative cover, good pool diversity, and little evidence of channel alteration all contribute to the high quality habitat observed here.

A new cross section was established for this site in 2017, due to the loss of the previous year’s pins. Establishing a new section made comparing the old data prior to 2016 impossible. However, between 2010 and 2016, an examination of that cross section data shows little alteration between 2015 and 2016. However, this site appears to have experienced significant sediment inputs between the 2011 and 2012 measurements as the thalweg elevation rose approximately 0.8 feet in that period. Elevations in-channel remained the same for 2013, but steady incision over the last three years has resulted in removal of approximately half of the in-channel sediment inputs observed for 2011 and 2012. Additionally, steady erosion of the right bank (downstream) and deposition on the left bank have been occurring since 2010, resulting in a channel that appears to be shifting towards the right bank while maintaining its approximate cross sectional area as it progresses. Significant erosion may occur if this trend continues as the channel is currently located along the downstream right edge of the stream valley. 

When comparing the cross sections of 2017 and 2018, very little change was observed. Attempts in future years to relocate the old pins will be made when sampling, but if they are unable to be found, the 2017 established pins will be used for all future comparisons.

DC-01 Cross Section Comparison 

Cross Section
Click to enlarge

Site DC-02: Habitat scores have been rising here since 2017 and appear to indicate improvement since monitoring commenced here in 2010. In 2018, an RBP score of 139 (Supporting) was measured, which is higher than both the cumulative average (114, Partially Supporting) and the 3-year average (131, Supporting). Improvements in scores for epifaunal substrate, sediment deposition, and bank stability appear to explain most of the increases.

DC-02 Cross Section Comparison 

Cross Section
Click to enlarge

Historical Data Summary:

YearBIBI (Condition)FIBI (Condition)RPB (Condition)
20102.71 (P)---147 (S)
20112.14 (P)---135 (S)
20122.43 (P)---150 (S)
20132.14 (P)---135 (S)
20141.86 (VP)---117 (PS)
2015---2.00 (P)151 (C)
20162.14 (P)1.33 (VP)132 (S)
20172.43 (P)---144 (S)
20182.43 (P)2.67 (P)135 (S)
YearBIBI (Condition)FIBI (Condition)RBP (Condition)
20103.00 (F)---87 (NS)
20112.71 (P)---110 (PS)
20122.71 (P)---104 (PS)
20132.43 (P)---106 (PS)
20142.43 (P)---93 (NS)
20153.00 (F)2.00 (P)132 (S)
20161.86 (VP)1.33 (VP)126 (S)
20171.86 (VP)---129 (S)
20181.29 (VP)2.00 (P)139 (S)
All Station Summary
 Average BIBI (SD)3-Year Average BIBI (SD)Average RPB (SD)3-Year Average RBP (SD)
DC-012.29 (0.26)2.33 (0.17)139 (11)137 (6)
DC-022.37 (0.58)1.67 (0.33)114 (18)131 (7)

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