Table 4.
List of Covariates Leading to an Average of at Least a 5% Reduction in Mean Square Error When Excluded From the Model
| Response variable | Covariates | Variable | Relative influence |
|---|---|---|---|
| CH4-D | National and local covariates | TOC | 15.7 |
| ag on slope > 10% | 14.6 | ||
| dissolved CH4 | 14.6 | ||
| reservoir area | 12.8 | ||
| TP | 12.4 | ||
| proportion <3 m deep | 5.9 | ||
| soil organic matter | 5.1 | ||
| CH4-D | National covariates | reservoir area | 23.0 |
| ag on slope > 10% | 14.3 | ||
| soil organic matter | 10.1 | ||
| percent ag | 9.4 | ||
| dynamic ratio | 8.4 | ||
| relative drainage area | 6.6 | ||
| depth ratio | 5.9 | ||
| proportion <3 m deep | 5.6 | ||
| CH4-E | National and local covariates | relative drainage area | 25.2 |
| proportion hypolimnetic | 17.4 | ||
| percent ag | 13.1 | ||
| dissolved CO2 | 9.3 | ||
| max depth | 9.1 | ||
| proportion hypoxic | 6.2 | ||
| CH4-E | National covariates | relative drainage area | 21.4 |
| percent ag | 15.3 | ||
| dynamic ratio | 10.3 | ||
| soil erodibility factor | 9.4 | ||
| ag on slope > 10% | 7.7 | ||
| proportion <3 m deep | 7.4 | ||
| depth ratio | 7.1 | ||
| max depth | 6.6 | ||
| mean air temperature | 6.3 | ||
| CH4-T | National and local covariates | soil organic matter | 29.7 |
| depth ratio | 11.8 | ||
| relative drainage area | 10.1 | ||
| percent ag | 8.0 | ||
| dissolved CO2 | 7.3 | ||
| ag on slope > 10% | 6.9 | ||
| proportion hypolimnetic | 5.7 | ||
| CH4-T | National covariates | relative drainage area | 21.6 |
| depth ratio | 20.0 | ||
| max depth | 16.6 | ||
| percent ag | 11.6 | ||
| proportion < 3 m deep | 7.0 | ||
| runoff | 5.1 | ||
| CO2-T | National and local covariates | dissolved CO2 | 47.4 |
| ag on slope > 10% | 14.5 | ||
| proportion hypoxic | 6.9 | ||
| percent ag | 6.1 | ||
| TP | 5.8 | ||
| CO2-T | National covariates | depth ratio | 23.8 |
| proportion < 3 m deep | 19.2 | ||
| runoff | 15.8 | ||
| relative drainage area | 9.2 | ||
| ag on slope > 10% | 7.8 | ||
| reservoir area | 6.9 | ||
| soil erodibility factor | 5.0 |
Note. These represent the most important variables in each boosted regression trees are listed in order of decreasing importance for each model.