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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.



2019 Summary Report:

Site DC-01
Time FrameBIBI (Condition)FIBI (Condition)RBP (Condition)
2019 Results1.00 (Very Poor)3--128 (Supporting)
Cumulative Average (2010-2019)2.14 (Poor)2.00 (Poor)2138 (Supporting)
3-year Running Average2.00 (Poor)2.00 (Poor)2135 (Supporting)
Site DC-02
Time FrameBIBI (Condition)FIBI (Condition)RBP (Condition)
2019 Results2.43 (Poor)--134 (Supporting)
Cumulative Average (2010-2019)2.37 (Poor)1.78 (Very Poor)2116 (Partially Supporting)
3-year Running Average1.86 (Poor)1.67 (Very Poor)2132 (Supporting)
1) No data for 2015.
2) No fish data for 2019. Cumulative and 3-Year Running Averages are through 2018.
3) Less than 60 bugs collected, automatically given score of Very Poor.

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 2019 BIBI score at this site is in the Very Poor range, at 1.00. This score is lower than in previous years due to the fact that it only got 12 organisms in its sample, automatically denoting a score of 1.00. Of the bugs that were collected, the sample was dominated by non-biting midges, which comprised approximately 50% of the insects found in 2019. Damselflies, dance flies, snails, and worms were the other types of bugs found in 2019. Past samples were largely dominated by worms with lesser amounts of non-biting midges present. It is unclear why this shift in organisms occurred in 2019, 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 score of 2.43, or Poor, in 2019. This represents a large decline since restoration, but a slight increase than the past few years. It is higher than both the cumulative average (2.37, Poor) and the three-year running average (1.86, Very 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 2019 sample seems to be synonymous with pre-restoration samples, aside from craneflies no longer making a presence after restoration occurred. However, all pre-restoration samples were dominated by non-biting midges, worms, and predacious diving beetles. The 2019 sample was very similar, but with much more snails observed. Ribbon worms also made a reappearance in 2019. 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: No fish were sampled in 2019. The 2018 results are described below.

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 and Geomorphic Assessments:

Site DC-01: Habitat conditions have been consistent since monitoring began here in 2010. In 2019, a habitat score of 128 (Supporting) was calculated for this site, which is consistent with the cumulative average (138, Supporting) and the 3-yr. running average (135, 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 years’ 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, 2018, and 2019, 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 consistent here since 2017 and appear to indicate improvement since monitoring commenced here in 2010. In 2019, an RBP score of 134 (Supporting) was measured, which is higher than both the cumulative average (116, Partially Supporting) and the 3-year average (132, Supporting). Improvements in scores for epifaunal substrate, channel flow status, and vegetative protection appear to explain most of the increases.

Between 2010 and 2019, erosion has taken place at the bottom of the channel of approximately 1.5 feet. This may have been due to the high amounts of rain that occurred during the 2018 years. The 2019 cross section shows some slight erosion of approximately 0.60 feet from 2018 and 2017.

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)
20191.00 (VP)--128 (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)
20192.43 (P)--134 (S)
All Station Summary
 Average BIBI (SD)3-Year Average BIBI (SD)Average RPB (SD)3-Year Average RBP (SD)
DC-012.14 (0.49)2.00 (0.68)138 (11)135 (7)
DC-022.37 (0.55)1.86 (0.47)116 (18)132 (5)

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