Chemical Monitoring
Trott Brook
| Monitoring Location | at Highway 63, Burns Township STORET SiteID = FordBrook_Hwy63 |
| Monitored By | ACD Staff |
| Years Monitored | 1998, 2003 and 2006 |
| Background: Trott Brook orginates in eastern Sherburne County, and flows eastward to the Rum River. The stream's watershed encompasses most of the northern part of the City of Ramsey. The City is working toward a network of greenways and trails that focus on the Trott Brook corridor. The monitoring site is just upstream of Trott Brook's confluence with Ford Brook. Stream biomonitoring is also conducted at this site. | |
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| Results and Discussion Eight water quality samples were taken in 2006, including four during storm events greater than one inch and four during baseflow (see figures and table below). Additionally, a limited number of water quality parameters were monitored on two other occasions. The primary water quality concerns identified include occasionally low dissolved oxygen and slightly elevated chlorides and conductivity. When Trott Brook was last monitored in 1998 and 2003 occasionally low dissolved oxygen (DO) was noted. In fact, a reason for the 2006 monitoring was to determine if a chronic problem existed. Combining the 2006 and previous monitoring reveals that occasionally low dissolved oxygen is a chronic problem. It has been below 5.0 mg/L (Minnesota Pollution Control Agency’s daily minimum standard for listing as “impaired”) on six of 23 times that it has been measured since 1998. An additional three measurements were between 5.0 and 5.5 mg/L. Put another way, DO was low 39.1% of the 23 observations. In 2006 DO was low only one of eight monitoring visits, but on that occasion it was 2.64 mg/L, which is low enough to negatively affect many types of stream life including most fish. That is especially concerning because Trott Brook is a tributary the Rum River, a major fishery, and probably serves as a spawning area for fish in the river. Larval fish are even more sensitive to low dissolved oxygen than adult fish. The cause of the low dissolved oxygen is unknown. One clue to the cause is that all of the <5.0 mg/L DO conditions occurred between June and August, when water temperatures were highest (19-22 C). Warm water can’t hold as much oxygen. In conditions of low flow and warm temperatures, DO can drop. However, this is not the sole cause for Trott Brook – if it were we would have seen many more low DO readings in 2006, a year with moderate drought and record-high monthly average temperatures. Moreover, the problem does not seem related to storm runoff or baseflow conditions, as half of the low DO measurements have occurred during storms and half during baseflow. The time of day that the DO measurements were taken also seems unrelated to the problem. Dissolved oxygen undergoes daily change patterns, typically lowest in the early morning. Time of day for most of the low DO measurements was not recorded, but those that are known were after 11am and it is very unlikely that any were taken before 9am. The information discussed above, in addition to the periodic nature of the problem leaves open the possibility that the cause of low dissolved oxygen is the periodic input of organic matter, such as wastewater or manure, entering the stream. It could even be a historic source, such as an old feedlot site. The decomposition of those materials consumes oxygen and is a common cause of low DO. A second, lesser, water quality concern for Trott Brook is conductivity and chlorides. Both of these were slightly elevated compared to other streams in Anoka County. Several other streams and ditches near Trott Brook have been found to have similar or worse conditions. In those cases in-depth studies revealed the cause was road deicing salts. These salts are infiltrating to the shallow water table which feeds the stream throughout the year. The consistent chloride levels during baseflow conditions suggest this is also occurring in Trott Brook. The chloride and conductivity levels observed are not high enough to impact stream life, but spikes during snowmelt (not monitored) could be higher. Other water quality parameters for Trott Brook were as good as or better than would be expected for a stream in this region of the state. Perhaps most notably, turbidity and suspended solids were usually low. One exception was 8/21/06 during baseflow when transparency and TSS were poor (turbidity was ok, suggesting particle size was small). |
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