基于刺槐年轮重建黄土丘陵区小流域年径流输沙研究

Reconstruction of annual runoff and sediment transport using tree-ring of black locust(Robinia pseudoacacia Linn.)in the Loess Hilly Region,China

刺槐是广泛分布于黄土高原的典型水土保持植物。以黄土丘陵区甘肃天水吕二沟小流域为研究区,分析了刺槐径向生长过程及其对气候因子的响应,并开展了利用刺槐年轮估算小流域年径流量、年输沙量的适用性评估。研究表明:(1)吕二沟刺槐人工林的径向生长随林龄呈明显的下降趋势,在幼龄林阶段(1—10 a)刺槐处于快速径向生长期((4.17±0.74)mm/a),之后逐渐下降,中龄林、成熟林、过熟林阶段(11—40 a)平均生长速率为(2.31±0.41)mm/a,较前期下降了44.60%。刺槐胸高断面积增量(BAI)在1—10 a平均以(5.46±2.13)cm^(2)/a的速度生长,在11—40 a仍保持上升趋势但年际间生长波动较大,生长速率平均为(10.80±1.95)cm^(2)/a,流域刺槐生长并未发生明显衰退。(2)刺槐的径向生长与温度多呈负相关,与降水、相对湿度及帕默尔干旱指数(PDSI)多呈正相关。其中刺槐径向生长与上年8月、9月(P<0.05)及当年7月均温、最高温呈显著负相关(P<0.01),与当年5月最低温呈显著正相关(P<0.05);与当年6月、7月降水量和上年8月、当年7月相对湿度呈显著正相关(P<0.05),与当年3月相对湿度显著负相关(P<0.05);与上年6月、上年10月—当年1月及当年3月—8月PDSI显著正相关(P<0.05),干旱胁迫明显抑制流域刺槐生长。(3)1978—2017年吕二沟流域年径流量、年输沙量呈减少趋势,年际间波动较大,存在明显丰枯阶段。流域径流输沙受降水量影响显著,且径流输沙显著正相关(P<0.001)。(4)利用刺槐年轮估算吕二沟流域年径流量、输沙量效果良好(P<0.02),方法可行。比较而言,相对自然条件下即人类干扰较少时径流输沙估算优于人类活动影响时期。利用树轮宽度反演水文过程可为缺乏水文观测资料区域提供参考。

The black locust(Robinia pseudoacacia Linn.)is a typical soil and water conservation plant widely distributed in Lvergou watershed of loess hilly area on the Loess Plateau.In this study,the radial growth of black locust and its response to climatic factors were investigated,and the applicability of estimating annual runoff and sediment transport in the watershed by using the ring width of black locust was evaluated.The results indicated that:(1)the radial growth of black locust plantation in Lvergou watershed showed an obvious downward trend with forest age.Black locust was in a rapid radial growth period((4.17±0.74)mm/a)in the young forest stages(1—10a)and then the radial growth gradually decreased,and the average growth rate of middle,mature and over-mature forest stages(11—40 a)was(2.31±0.41)mm/a,which decreased by 44.60%compared with the previous period.Basal area increment(BAI)of black locust increased at an average rate of(5.46±2.13)cm^(2)/a from 1—10 a,then kept an upward trend from 11—40 a,but its annual growth fluctuated greatly,with an average growth rate of(10.80±1.95)cm^(2)/a.(2)The radial growth of black locust was negatively correlated with temperature,and positively correlated with precipitation,relative humidity and Palmer Drought Index(PDSI).The radial growth of black locust was negatively correlated with the mean temperature and maximum temperature in August,September(P<0.05)of previous year,July(P<0.01)of current year,and positively correlated with the minimum temperature in May(P<0.05)of current year.It was significantly positively correlated with the precipitation in June and July of current year and the relative humidity in August of previous year and July of current year(P<0.05),and significantly negatively correlated with the relative humidity in March of current year(P<0.05).The growth of black locust was positively correlated with PDSI in June of previous year,October of previous year to January of current year and March to August of current year(P<0.05),which means that drought stress inhibited the growth of black locust significantly.(3)From 1978 to 2017,the annual runoff and sediment transport in the Lvergou watershed showed a decreasing trend,and the inter-annual fluctuation was large,with an obvious period of wet and dry.The runoff and sediment transport were significantly affected by precipitation,and the runoff and sediment transport were positively correlated(P<0.001).(4)Our results indicated that using black locust tree rings to estimate the annual runoff and sediment transport in Lvergou watershed was effective(P<0.02),and the method was feasible.In comparison,the estimation of runoff and sediment transport under natural conditions was better than that of under the influence of human activities.Our research findings demonstrate that tree ring analysis can be employed as a valuable tool for estimating hydrological data in regions where such observations are limited or unavailable.