- Pond Productivity
- Drivers of Change
- Interactive Map
- HRUs
- Takeaways
Pond Productivity
Pond productivity refers to the amount of biological activity, particularly the growth of algae plants, that occurs in a pond, driven by the availability of nutrients and environmental conditions. Limiting nutrients to or within a pond can limit its productivity. These nutrients can enter the pond via the watershed or groundwater. In a freshwater system, the limiting nutrient is usually phosphorus, which means that the amount of algal growth in a lake is determined by the amount of phosphorus in the lake. However, there are other factors at play in these ecosystems that affect productivity, including the depth and volume of a pond, the residence time of the pond water (the amount of time water stays in a pond), the weather, and the mixing (or stratification) depth. The amount of production in a lake affects lake biology as a whole.
The trophic state index (TSI) is a measure of productivity, as reflected by abundance of algae. Per guidance from the North American Lake Management Society protocol (Carlson & Simpson, 1996), TSI is calculated from three different measurements: Secchi disk depth, chlorophyll a, or total phosphorus. Given the availability of measured total phosphorus in previously collected Pond and Lake Stewardship program data, surface total phosphorus was used to calculate the Carlson TSI.
The trophic state index is rated on a scale from 0 to 100.
0–40: Oligotrophic
relatively low in plant nutrients, with abundant oxygen in deeper waters.
40-50: Mesotrophic
having a moderate amount of nutrients. More organic matter is present, water is less clear.
50–70: Eutrophic
rich in nutrients and thereby supporting a dense plant population, the decomposition of which uses oxygen, adversely impacting or killing animal life.
70–100: Hypereutrophic
extremely rich in nutrients, resulting in severe impacts to pond ecology.
Drivers of Change
Activities on the land and characteristics of a watershed may have potentially negative impacts on a pond’s water quality and ecosystem health. These activities and characteristics that have a negative impact are referred to as stressors. For example, a cranberry bog adjacent to a pond could be a stressor, as nutrients from fertilizers used to grow cranberries could be released into the pond. Similarly, golf courses may produce runoff carrying fertilizers and pesticides that travel to nearby ponds over the ground or through the groundwater.
Commission staff identified potential stressors using GIS data and our understanding of ponds. Factors that may have a detrimental impact on a pond were given a score of one, and factors that do not have a detrimental impact on ponds or may even help a pond to cope with a stressor, such as a centralized sewer system, were given a score of zero. Other more complex factors, such as the amount of impervious cover, were assigned a score on a scale. The scores were summed up, resulting in a cumulative stressor score for each pond, ranging from 2 (minimal stress) to 20 (highly stressed).
The most stressed ponds should be considered high priorities for monitoring and restoration activities, while the least stressed ponds should be considered for protection strategies. The most and least stressed ponds on Cape Cod are listed below.
| Most Stressed Ponds | Town | Score | Least Stressed Ponds | Town | Score |
| Long Pond | Yarmouth |
20 |
Doanes Bog Pond |
Wellfleet |
2 |
| Bucks Pond | Harwich | 20 | Small Pond | Hyannis | 2 |
| Wequaquet Lake | Barnstable | 20 | Beccas Pond | Mashpee | 3 |
| James Pond | Yarmouth | 19 | Clapps Round Pond | Provincetown | 3 |
| Jenkins Pond | Falmouth | 19 | Spectacle Pond | Wellfleet | 3 |
| Flax Pond | Bourne | 19 | Angel Mirror Pond | Falmouth | 3 |
| Johns Pond | Mashpee | 19 | The Basin | Bourne | 3 |
| Dean's Pond | Mashpee | 19 | Miller Pond | Yarmouth | 3 |
| Lake Elizabeth | Barnstable | 18 | Cash Pond | Dennis | 3 |
| Peters Pond | Sandwich | 18 | 1858 Bog | Brewster | 3 |
| Long Pond | Barnstable | 18 | |||
| Ashumet Pond | Mashpee | 18 |
Interactive Map
This interactive map shows all of the ponds on Cape Cod ranked by their cumulative stressor score.
From a regional perspective, a possible way forward to manage the ponds based on their cumulative stressor score could include the following tiered approach. Towns may have additional criteria to help prioritize ponds for action, as well as funding and logistical considerations.
Minimally stressed (1-5): Develop a management plan to protect the ponds.
Some stress (6-10): Continue monitoring to ensure the pond does not further degrade while also developing a plan to protect the pond.
Stressed (11-15): Determine possible remediation projects that can be quickly implemented, such as stormwater management practices, and assess priorities for future management. Continue monitoring.
Highly stressed (16-20): Prioritize for mitigation. Identify and implement major rehabilitation strategies to reduce or remove stressors. Continue monitoring.
Hydrologic Response Units
To help identify ponds where immediate, meaningful action may be taken, the hydrologic response unit (HRU) hotspots on a pond shore can be referenced to locate where stormwater management solutions should be considered.
The HRU tool generated the flow rate, the load of total suspended solids, total phosphorus, and total nitrogen. These stressors were included in the cumulative stressor score, and for this study were also mapped (Figure 1). Figure 1 (below) shows hotspots along pond shorelines where impervious surfaces (e.g., roads, boat ramps) and phosphorus loading hotspots intersect. These locations will need to be ground-truthed as the HRU tool does not take into consideration existing stormwater management practices.
Figure 1. Cape-wide HRU phosphorous loading hotspots where impervious surfaces are within 100 feet of the pond shore.
Takeaways
There are many factors involved in a pond’s healthy ecosystem, and the GIS analysis conducted as part of the Freshwater Initiative considered a limited set based on available data. The ponds with the highest scores aren’t necessarily the ponds with the highest trophic status. There are likely stressors that have not been quantified in the cumulative stressor score, as well as other variables that help a pond cope with stressors, such as short residence time and volume of a pond. Some of these variables that help a pond manage stressors were not included because the information is not available for all ponds; inclusion for some ponds and not others would skew the scores.
This study and the regional pond analysis have helped us understand that more data are needed, and more research needs to be done, including filling critical data gaps:
- Numerous ponds don’t have recorded maximum or average depths
- Pond volumes should be calculated and watersheds delineated so volume-to-watershed ratios can be determined for all ponds monitored
- Groundwater quality, specifically the concentration of total phosphorus is needed.
Regardless of pond health, there are easy-to-implement strategies that would benefit a pond. The HRU tool used in this project located phosphorus loading hotspots on pond shores (Hydrologic Response Unit tab (Figure 1)). Towns could reference this map to implement stormwater control measures.
For a deeper dive into this study, please see the Pond Characteristics Memo.
